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Power rule

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51010712
Find the slope of the tangent line to \(y=0.2x^2+5x-1\) at \(x=5\).

Hints

- What does the derivative represent at a point? - Differentiate each term of the function. - Substitute \(x=5\) into the derivative.

Solution

1. Differentiate the function: \(y'=0.4x+5\). 2. Evaluate the derivative at \(x=5\): \(y'(5)=0.4\cdot 5+5\). 3. Simplify: \(y'(5)=2+5=7\).

Answer

\(7\)
52222312
Let \(f(x)=-x^2+4x-2\). a) Find the derivative function \(f'\). b) Find the point \(P(x_0,f(x_0))\) where the graph of \(f\) has a horizontal tangent. c) Find the point \(Q(q,f(q))\) where the slope of the graph is \(6\).

Hints

- What derivative value corresponds to a horizontal tangent? - Set the derivative equal to the required slope. - After finding an x-coordinate, substitute it into the original function to find the y-coordinate.

Solution

1. Differentiate using the power, constant, and sum rules: \(f'(x)=-2x+4\). 2. A horizontal tangent has slope \(0\), so solve \(-2x_0+4=0\). This gives \(x_0=2\). 3. Evaluate the function: \(f(2)=-(2)^2+4\cdot 2-2=2\). Therefore, \(P=(2,2)\). 4. For slope \(6\), solve \(-2q+4=6\). This gives \(q=-1\). 5. Evaluate the function: \(f(-1)=-(-1)^2+4(-1)-2=-7\). Therefore, \(Q=(-1,-7)\).

Answer

a) \(f'(x)=-2x+4\) b) \(P=(2,2)\) c) \(Q=(-1,-7)\)
52223112
Find the derivative function \(f'\) for each function. a) \(f(x)=\frac{1}{4}x^4-2x^3+5x\) b) \(f(x)=\frac{2}{3}x^6+\sqrt{5}x^2-\pi\) c) \(f(x)=kx^n+2x\), where \(k\in\mathbb{R}\), \(n\in\mathbb{N}\), and \(n\geq1\)

Hints

- Differentiate each term separately using the power, constant-multiple, and sum rules. - What is the derivative of a term that does not contain the variable? - Treat \(k\) and \(n\) as parameters and \(\pi\) as a constant.

Solution

1. Differentiate each term in part a): \(f'(x)=\frac{1}{4}(4x^3)-2(3x^2)+5=x^3-6x^2+5\). 2. Differentiate each term in part b). The constant term has derivative \(0\): \(f'(x)=\frac{2}{3}(6x^5)+2\sqrt{5}x=4x^5+2\sqrt{5}x\). 3. Treat \(k\) and \(n\) as constants in part c): \(f'(x)=knx^{n-1}+2\).

Answer

a) \(f'(x)=x^3-6x^2+5\) b) \(f'(x)=4x^5+2\sqrt{5}x\) c) \(f'(x)=knx^{n-1}+2\)
52223212
Find the derivative function \(f'\) for each function. a) \(f(x)=\frac{x^3-6x}{3}\) b) \(f(x)=(x+3)^2\) c) \(f(x)=a^2x^2+ax+1\), where \(a\in\mathbb{R}\) is a parameter

Hints

- Rewrite each expression as a sum of simple power functions before differentiating. - Expand the squared binomial in part b). - Identify the variable of differentiation and treat every parameter as a constant.

Solution

1. Rewrite part a) as \(f(x)=\frac{1}{3}x^3-2x\). Then \(f'(x)=x^2-2\). 2. Expand part b): \(f(x)=x^2+6x+9\). Therefore, \(f'(x)=2x+6\). 3. In part c), treat \(a\) as a constant. Then \(f'(x)=2a^2x+a\).

Answer

a) \(f'(x)=x^2-2\) b) \(f'(x)=2x+6\) c) \(f'(x)=2a^2x+a\)
52223312
Find the derivative function \(f'\) for \(f(x)=\frac{1}{2}x^4-4x^3+12x-5\).

Hints

- Use the constant-multiple rule when a coefficient multiplies a power of \(x\). - In the power rule, how does the exponent change? - What is the derivative of a constant? - Differentiate a sum term by term.

Solution

1. Apply the power rule to the first term: \(\frac{d}{dx}\left(\frac{1}{2}x^4\right)=2x^3\). 2. Differentiate the second term: \(\frac{d}{dx}(-4x^3)=-12x^2\). 3. The derivative of \(12x\) is \(12\), and the derivative of \(-5\) is \(0\). 4. Combine the results: \(f'(x)=2x^3-12x^2+12\).

Answer

\(f'(x)=2x^3-12x^2+12\)
52223512
Find the first derivative of each function. a) \(f(x)=0.2x^5-3x^2+8\) b) \(f(t)=\frac{1}{4}t^4-\frac{2}{3}t^3+7t\) c) \(f(x)=mx^2+nx+p\), where \(m\), \(n\), and \(p\) are constants d) \(f(k)=x^3k^2-5k\), where \(x\in\mathbb{R}\) is a parameter

Hints

- Differentiate only with respect to the variable shown in the function notation. - A constant term has derivative \(0\). - For the power rule, multiply by the exponent and then decrease the exponent by \(1\). - Treat parameters as constants.

Solution

1. For part a), apply the power rule term by term: \(f'(x)=x^4-6x\). 2. For part b), differentiate with respect to \(t\): \(f'(t)=t^3-2t^2+7\). 3. For part c), treat \(m\), \(n\), and \(p\) as constants: \(f'(x)=2mx+n\). 4. For part d), differentiate with respect to \(k\) and treat \(x^3\) as a constant coefficient: \(f'(k)=2x^3k-5\).

Answer

a) \(f'(x)=x^4-6x\) b) \(f'(t)=t^3-2t^2+7\) c) \(f'(x)=2mx+n\) d) \(f'(k)=2x^3k-5\)
52223612
Differentiate each function with respect to the variable shown. a) \(f(z)=\frac{1}{6}z^3-z^2+\frac{1}{2}z\) b) \(f(x)=4x^7-2ax^3\) c) \(s(t)=vt+s_0\) d) \(f(x)=x^3k^2-5k\), where \(k\in\mathbb{R}\) is a parameter

Hints

- For each term, decide whether it contains the variable of differentiation. - A term that does not contain the variable has derivative \(0\). - Simplify numerical coefficients after applying the power rule. - In part d), \(x\) is the variable and \(k\) is a parameter.

Solution

1. For part a), differentiate term by term: \(f'(z)=\frac{1}{2}z^2-2z+\frac{1}{2}\). 2. In part b), treat \(a\) as a constant: \(f'(x)=28x^6-6ax^2\). 3. In part c), \(v\) and \(s_0\) are constants, so \(s'(t)=v\). 4. In part d), treat \(k\) as a constant. Since \(-5k\) does not contain \(x\), its derivative is \(0\), and \(f'(x)=3k^2x^2\).

Answer

a) \(f'(z)=\frac{1}{2}z^2-2z+\frac{1}{2}\) b) \(f'(x)=28x^6-6ax^2\) c) \(s'(t)=v\) d) \(f'(x)=3k^2x^2\)
52224112
Find the derivative function \(f'\) for \(f(x)=\frac{5}{6}x^6-2x^3+0.4x^2-9\).

Hints

- Differentiate a sum one term at a time. - Apply the power rule to both the exponent and coefficient. - A constant has derivative \(0\). - Treat a decimal coefficient the same way as any other constant coefficient.

Solution

1. Differentiate each power term: \(\frac{d}{dx}\left(\frac{5}{6}x^6\right)=5x^5\), \(\frac{d}{dx}(-2x^3)=-6x^2\), and \(\frac{d}{dx}(0.4x^2)=0.8x\). 2. The derivative of \(-9\) is \(0\). 3. Combine the terms: \(f'(x)=5x^5-6x^2+0.8x\).

Answer

\(f'(x)=5x^5-6x^2+0.8x\)
52224212
The family of functions \(g_a\), with parameter \(a\neq0\), is defined by \(g_a(t)=\frac{a}{3}t^3-\frac{1}{a}t^2+5t\). Find a formula for \(g_a'\).

Hints

- What role does \(a\) play when differentiating with respect to \(t\)? - The power rule still applies when a coefficient contains a parameter. - What is the derivative of the linear term \(5t\)? - Since \(a\) is part of a constant coefficient, it remains in the denominator.

Solution

1. Differentiate with respect to \(t\), treating \(a\) as a constant. 2. The first term gives \(at^2\), the second gives \(-\frac{2}{a}t\), and the third gives \(5\). 3. Therefore, \(g_a'(t)=at^2-\frac{2}{a}t+5\).

Answer

\(g_a'(t)=at^2-\frac{2}{a}t+5\)
52225112
Let \(f(x)=\frac{1}{3}x^3-4x^2+7x-5\). A student claims that \(f'(x)=x^2-8x+7x\). Describe the error in differentiating \(7x\), and find the correct derivative function.

Hints

- What is the derivative of a term of the form \(cx\)? - How does the exponent change under the power rule? - Check every term of the original function separately.

Solution

1. The student left the variable in the derivative of the linear term. Since \(\frac{d}{dx}(x)=1\), the derivative of \(7x\) is \(7\), not \(7x\). 2. Differentiate all terms: \(\frac{d}{dx}\left(\frac{1}{3}x^3\right)=x^2\), \(\frac{d}{dx}(-4x^2)=-8x\), \(\frac{d}{dx}(7x)=7\), and \(\frac{d}{dx}(-5)=0\). 3. Therefore, \(f'(x)=x^2-8x+7\).

Answer

The derivative of \(7x\) is \(7\), not \(7x\). The correct derivative is \(f'(x)=x^2-8x+7\).
52225212
Each derivative below contains an error. (1) \(g(x)=\frac{1}{2}x^4-2x^2+12\) and the claimed derivative is \(g'(x)=2x^3-4x+12\). (2) \(h(x)=2x^5-\frac{3}{x^2}\) and the claimed derivative is \(h'(x)=10x^4-6x^{-3}\). Explain each error briefly and give the correct derivative function.

Hints

- What is the derivative of a term that does not contain \(x\)? - Rewrite a power of \(x\) in the denominator using a negative exponent. - When applying the power rule to a negative exponent, check the signs in the coefficient multiplication.

Solution

1. In (1), the constant rule was applied incorrectly. The derivative of \(12\) is \(0\), so \(g'(x)=2x^3-4x\). 2. In (2), rewrite \(-\frac{3}{x^2}\) as \(-3x^{-2}\). Its derivative is \((-3)(-2)x^{-3}=6x^{-3}\), so \(h'(x)=10x^4+6x^{-3}=10x^4+\frac{6}{x^3}\).

Answer

(1) The constant \(12\) should have derivative \(0\). The correct derivative is \(g'(x)=2x^3-4x\). (2) The sign is wrong because \((-3)(-2)=6\). The correct derivative is \(h'(x)=10x^4+6x^{-3}\), or \(h'(x)=10x^4+\frac{6}{x^3}\).
52228312
Let \(f(x)=x^3-3x^2+2\). Find an equation of the tangent line to the graph of \(f\) at \(x=1\).

Hints

- Substitute the given x-value into the function to find the point of tangency. - The derivative gives the slope of the tangent line. - Use point-slope form after finding the point and slope. - A tangent line matches the curve's instantaneous slope at the point of tangency.

Solution

1. Find the point of tangency: \(f(1)=1^3-3(1)^2+2=0\), so the point is \((1,0)\). 2. Differentiate: \(f'(x)=3x^2-6x\). 3. Find the tangent slope: \(f'(1)=3(1)^2-6(1)=-3\). 4. Use point-slope form: \(y-0=-3(x-1)\). 5. Simplify: \(y=-3x+3\).

Answer

\(y=-3x+3\)
52228412
Let \(f(x)=0.5x^2-2x+4\). Find the equation of the normal line \(n\) to the graph of \(f\) at \(x_0=4\).

Hints

- First find the point through which the normal line passes. - Tangent and normal slopes are negative reciprocals. - Use the derivative to find the tangent slope. - Substitute the slope and point into a line equation.

Solution

1. Find the point: \(f(4)=0.5\cdot4^2-2\cdot4+4=4\), so the point is \((4,4)\). 2. Differentiate: \(f'(x)=x-2\). The tangent slope is \(f'(4)=2\). 3. The normal slope is the negative reciprocal: \(m_n=-\frac{1}{2}\). 4. Use point-slope form: \(y-4=-\frac{1}{2}(x-4)\), so \(y=-0.5x+6\).

Answer

\(n: y=-0.5x+6\)
52229512
Find an equation of the tangent line to \(f(x)=0.5x^4-3x^2+4\) at \(x=2\).

Hints

- A line is determined by its slope and one point. - Use the derivative to find the curve's slope at \(x=2\). - Substitute \(x=2\) into the original function to find the point of tangency. - Use point-slope form to write the line equation.

Solution

1. Find the point of tangency: \(f(2)=0.5\cdot 2^4-3\cdot 2^2+4=0\), so the point is \((2,0)\). 2. Differentiate: \(f'(x)=2x^3-6x\). 3. Find the tangent slope: \(f'(2)=2\cdot 2^3-6\cdot 2=4\). 4. Use point-slope form: \(y-0=4(x-2)\). 5. Simplify: \(y=4x-8\).

Answer

\(y=4x-8\)
52229712
Let \(f(x)=-0.5x^3+2x^2-3\). Find the angle, measured counterclockwise from the positive x-axis, that the tangent line at \(x=1\) makes with the x-axis. Round to the nearest tenth of a degree.

Hints

- The derivative at a point gives the tangent line's slope. - How are a line's slope \(m\) and its angle \(\alpha\) related? - Use degree mode when evaluating the inverse tangent.

Solution

1. Differentiate: \(f'(x)=-1.5x^2+4x\). 2. Find the tangent slope at \(x=1\): \(m=f'(1)=-1.5(1)^2+4(1)=2.5\). 3. The angle \(\alpha\) satisfies \(\tan(\alpha)=m\), so \(\alpha=\arctan(2.5)\). 4. In degree mode, \(\alpha\approx 68.2^\circ\).

Answer

\(68.2^\circ\)
52230712
Let \(f(x)=\frac{1}{3}x^3-x^2-2x\). Find an equation of the tangent line to the graph of \(f\) at \(x=3\). Then find the angle that the tangent line makes with the positive x-axis.

Hints

- The derivative at a point gives the tangent line's slope. - Use point-slope form to write the tangent line. - Relate a line's slope to its angle with the positive x-axis.

Solution

1. Find the point of tangency: \(f(3)=\frac{1}{3}\cdot 3^3-3^2-2\cdot 3=-6\), so the point is \((3,-6)\). 2. Differentiate: \(f'(x)=x^2-2x-2\). 3. Find the slope: \(f'(3)=3^2-2\cdot 3-2=1\). 4. Use point-slope form: \(y+6=x-3\), so \(y=x-9\). 5. Since \(\tan(\alpha)=1\), the angle is \(\alpha=45^\circ\).

Answer

The tangent line is \(y=x-9\), and its angle with the positive x-axis is \(45^\circ\).
52231312
Let \(f(x)=x^3-4x^2+5\). Find an equation of the tangent line to the graph of \(f\) at \(P=(1,f(1))\).

Hints

- A line is determined by a point and a slope. - Use the derivative to find the tangent slope. - First calculate the complete point of tangency. - Use point-slope form to write the line.

Solution

1. Find the point of tangency: \(f(1)=1^3-4(1)^2+5=2\), so \(P=(1,2)\). 2. Differentiate: \(f'(x)=3x^2-8x\). 3. Find the tangent slope: \(f'(1)=3(1)^2-8(1)=-5\). 4. Use point-slope form: \(y-2=-5(x-1)\). 5. Simplify: \(y=-5x+7\).

Answer

\(y=-5x+7\)
52231512
Find the equation of the normal line \(n\) to the graph of \(f(x)=x^2-4x+1\) at \(x_0=3\).

Hints

- Evaluate the function to find the point on the graph. - Tangent and normal slopes are negative reciprocals. - Use point-slope form after finding the normal slope.

Solution

1. Find the point: \(f(3)=3^2-4\cdot3+1=-2\), so the point is \((3,-2)\). 2. Differentiate: \(f'(x)=2x-4\). The tangent slope is \(f'(3)=2\). 3. The normal slope is \(-\frac{1}{2}\). 4. Use point-slope form: \(y+2=-\frac{1}{2}(x-3)\), so \(y=-0.5x-0.5\).

Answer

\(n: y=-0.5x-0.5\)
52231612
Let \(f(x)=\frac{1}{4}x^3+x\). Find the equation of the normal line to the graph of \(f\) at \(P(2,f(2))\).

Hints

- Use the derivative to find the tangent slope at the given point. - The normal line is perpendicular to the tangent line. - Perpendicular nonvertical lines have slopes whose product is \(-1\).

Solution

1. Find the point: \(f(2)=\frac{1}{4}\cdot2^3+2=4\), so \(P=(2,4)\). 2. Differentiate: \(f'(x)=\frac{3}{4}x^2+1\). The tangent slope is \(f'(2)=4\). 3. The normal slope is \(-\frac{1}{4}\). 4. Use point-slope form: \(y-4=-\frac{1}{4}(x-2)\), so \(y=-0.25x+4.5\).

Answer

\(n: y=-0.25x+4.5\)
52235312
Let \(f(x)=x^2+x+1\) and \(g(x)=-x^2+5x-1\). 1. Show algebraically that the graphs of \(f\) and \(g\) are tangent to each other at \(x=1\). 2. Find an equation of their common tangent line at that point.

Hints

- What must be true about the function values for two graphs to meet at a point? - What must also be true about their derivatives for the graphs to be tangent there? - Use point-slope form for the common tangent line.

Solution

1. The function values agree: \(f(1)=1+1+1=3\) and \(g(1)=-1+5-1=3\). Thus, both graphs pass through \((1,3)\). 2. Differentiate: \(f'(x)=2x+1\) and \(g'(x)=-2x+5\). 3. The slopes also agree at \(x=1\): \(f'(1)=3\) and \(g'(1)=3\). Therefore, the graphs are tangent at \((1,3)\). 4. The common tangent line has slope \(3\) and passes through \((1,3)\): \(y-3=3(x-1)\), so \(y=3x\).

Answer

1. Both graphs pass through \((1,3)\), and \(f'(1)=g'(1)=3\), so they are tangent there. 2. \(y=3x\)
52236312
Let \(f(x)=\frac{1}{2}x^3-2x\). Find the equation of the normal line \(n\) to the graph of \(f\) at \(x_0=2\).

Hints

- Evaluate the function to find the point on the graph. - Use the derivative for the tangent slope. - The normal slope is the negative reciprocal of the tangent slope. - Write the line using its slope and the point.

Solution

1. Find the point: \(f(2)=\frac{1}{2}\cdot2^3-2\cdot2=0\), so the point is \((2,0)\). 2. Differentiate: \(f'(x)=\frac{3}{2}x^2-2\). The tangent slope is \(f'(2)=4\). 3. The normal slope is \(-\frac{1}{4}\). 4. Use point-slope form: \(y=-\frac{1}{4}(x-2)\), so \(y=-0.25x+0.5\).

Answer

\(n: y=-0.25x+0.5\)
52240712
Find the derivative of each function. a) \(f(x)=0.4x^5-2x^3+9\) b) \(g(t)=\frac{1}{6}t^3-\frac{3}{4}t^2+t\) c) \(h(x)=k^2x^2-2kx\), where \(k\in\mathbb{R}\)

Hints

- Identify the variable and treat all parameters as constants. - A constant term has derivative \(0\). - Apply the constant-multiple rule to each power term. - Differentiate a sum term by term.

Solution

1. For part a), differentiate term by term: \(f'(x)=2x^4-6x^2\). 2. For part b), \(g'(t)=\frac{1}{2}t^2-\frac{3}{2}t+1\). 3. For part c), treat \(k\) as a constant: \(h'(x)=2k^2x-2k\).

Answer

a) \(f'(x)=2x^4-6x^2\) b) \(g'(t)=\frac{1}{2}t^2-\frac{3}{2}t+1\) c) \(h'(x)=2k^2x-2k\)
52240812
Find the derivative of each function. Simplify before differentiating when helpful. a) \(f(x)=(x^2-5)(x+2)\) b) \(g(x)=\frac{1}{4}x^4-\frac{2}{3}x^3+\pi\) c) \(h(z)=cz^3-\frac{1}{c}z\), where \(c\neq0\)

Hints

- Can you rewrite the expression as a sum of simple powers before differentiating? - A term with no variable has derivative \(0\). - Fractions and symbols such as \(\pi\) can be constant coefficients or constant terms.

Solution

1. Expand part a): \(f(x)=x^3+2x^2-5x-10\). Then \(f'(x)=3x^2+4x-5\). 2. Differentiate part b) term by term. Since \(\pi\) is constant, \(g'(x)=x^3-2x^2\). 3. In part c), differentiate with respect to \(z\), treating \(c\) and \(\frac{1}{c}\) as constants: \(h'(z)=3cz^2-\frac{1}{c}\).

Answer

a) \(f'(x)=3x^2+4x-5\) b) \(g'(x)=x^3-2x^2\) c) \(h'(z)=3cz^2-\frac{1}{c}\)
52260712
Let \(f(x)=0.25x^2+x-3\). Find an equation of the tangent line to the graph of \(f\) that is parallel to \(y=2x+5\).

Hints

- Parallel lines have equal slopes. - Set the derivative equal to the slope of the given line. - Find the point of tangency after finding its x-coordinate. - Use point-slope form to write the line.

Solution

1. Differentiate: \(f'(x)=0.5x+1\). 2. A parallel tangent must have slope \(2\), so solve \(0.5x+1=2\). This gives \(x=2\). 3. Find the point of tangency: \(f(2)=0.25(2)^2+2-3=0\), so the point is \((2,0)\). 4. Write the tangent line: \(y-0=2(x-2)\), so \(y=2x-4\).

Answer

\(y=2x-4\)
52279912
Consider the family \(f_a(x)=ax^2-4x+1\), where \(a\in\mathbb{R}\). a) Find \(a\) so that the graph passes through \(P=(2,5)\). b) Find the slope of the tangent line at \(x=0\). c) Find \(a\) so that the tangent line at \(x=1\) has slope \(10\).

Hints

- Substitute a point into the function to require that it lies on the graph. - Differentiate while treating the parameter as a constant. - A specified tangent slope gives an equation involving the derivative. - Notice whether the derivative at a given input depends on the parameter.

Solution

1. For the graph to pass through \((2,5)\), require \(5=4a-8+1\). Thus, \(4a=12\), so \(a=3\). 2. Differentiate: \(f_a'(x)=2ax-4\). At \(x=0\), \(f_a'(0)=-4\), independent of \(a\). 3. For slope \(10\) at \(x=1\), solve \(f_a'(1)=10\): \(2a-4=10\). Thus, \(a=7\).

Answer

a) \(a=3\) b) \(-4\) c) \(a=7\)
52291712
Find the derivative of \(f(x)=0.2x^5-\frac{3}{4}x^4+7x-\sqrt{2}\).

Hints

- Apply the power rule to each term separately. - What happens to a constant term that does not contain \(x\)? - Treat decimal and fractional coefficients as constant factors.

Solution

1. Differentiate each term using the power, constant-multiple, and sum rules. 2. The constant term has derivative \(0\), so \(f'(x)=x^4-3x^3+7\).

Answer

\(f'(x)=x^4-3x^3+7\)
52291812
Find each derivative. The letters \(a\) and \(k\) represent real constants. a) \(h(x)=\frac{1}{a}x^3+ax^2-a^3x+10\), where \(a\neq0\) b) \(p(t)=(3t-k)^2\)

Hints

- Identify the variable of differentiation and treat the other letters as constants. - A parameter multiplying a power remains as a constant coefficient. - A term without the variable has derivative \(0\). - Expanding the squared binomial may simplify part b).

Solution

1. In part a), differentiate with respect to \(x\) and treat \(a\) as a constant: \(h'(x)=\frac{3}{a}x^2+2ax-a^3\). 2. For part b), expand first: \(p(t)=9t^2-6kt+k^2\). 3. Differentiate with respect to \(t\), treating \(k\) as a constant: \(p'(t)=18t-6k\).

Answer

a) \(h'(x)=\frac{3}{a}x^2+2ax-a^3\) b) \(p'(t)=18t-6k\)
52548912
Find the derivative of the family of functions \(f_k(x)=\frac{1}{2k}x^4-k^2x^2+7k\), where \(k\in\mathbb{R}\setminus\{0\}\).

Hints

- Decide which symbol is the variable and which is treated as a constant. - Differentiate the sum term by term. - What is the derivative of a term that contains no \(x\)?

Solution

1. Treat \(k\) as a constant and differentiate each term. 2. By the power rule, \(\frac{d}{dx}\left(\frac{1}{2k}x^4\right)=\frac{2}{k}x^3\). 3. Also, \(\frac{d}{dx}(-k^2x^2)=-2k^2x\), and \(\frac{d}{dx}(7k)=0\). 4. Therefore, \(f_k'(x)=\frac{2}{k}x^3-2k^2x\).

Answer

\(f_k'(x)=\frac{2}{k}x^3-2k^2x\)
52639112
Let \(f(x)=-\frac{1}{2}x^2+3\). 1. Find the slope of the tangent line at \(x=1\). 2. Find the angle \(\alpha\), in the interval \([0^\circ,180^\circ)\), that the tangent line makes with the positive x-axis. 3. Find an equation of the tangent line at \(B=(1,f(1))\).

Hints

- The derivative gives the tangent slope. - Use the tangent function to relate slope and angle. - Find the point of tangency from the original function. - Use point-slope form to write the tangent line.

Solution

1. Differentiate: \(f'(x)=-x\). Therefore, the slope at \(x=1\) is \(f'(1)=-1\). 2. Since \(\tan(\alpha)=-1\) and \(\alpha\in[0^\circ,180^\circ)\), \(\alpha=135^\circ\). 3. The point of tangency is \((1,f(1))=(1,2.5)\). Using slope \(-1\), \(y-2.5=-(x-1)\), so \(y=-x+3.5\).

Answer

1. \(-1\) 2. \(135^\circ\) 3. \(y=-x+3.5\)
52639712
Find the first derivative of each function. a) \(f(x)=0.5x^6-4x^3+2x-10\) b) \(f(x)=\frac{2}{3}x^3-\frac{1}{2}x^2+\pi\) c) \(f(x)=(2x-1)x^2\) For part c), also find the slope of the graph at \(x=2\).

Hints

- Expanding a product can turn it into a sum of powers. - A constant term has derivative \(0\). - The value of the derivative at a given input is the graph's slope there.

Solution

1. For part a), differentiate term by term: \(f'(x)=3x^5-12x^2+2\). 2. For part b), the constant \(\pi\) has derivative \(0\), so \(f'(x)=2x^2-x\). 3. For part c), expand: \(f(x)=2x^3-x^2\). Then \(f'(x)=6x^2-2x\). 4. Evaluate at \(x=2\): \(f'(2)=6(2)^2-2(2)=20\).

Answer

a) \(f'(x)=3x^5-12x^2+2\) b) \(f'(x)=2x^2-x\) c) \(f'(x)=6x^2-2x\); the slope at \(x=2\) is \(20\).
52639912
Let \(f(x)=2x^2-8x+5\). a) Find the slope of the graph at \(x=3\). b) Find an equation of the tangent line at \(x=3\).

Hints

- The derivative gives the slope at a point. - A tangent line requires both a point and a slope. - The tangent and the curve have the same slope at the point of tangency.

Solution

1. Differentiate: \(f'(x)=4x-8\). 2. Evaluate the derivative: \(f'(3)=4(3)-8=4\). 3. Find the point of tangency: \(f(3)=2(3)^2-8(3)+5=-1\), so the point is \((3,-1)\). 4. Use point-slope form: \(y+1=4(x-3)\), so \(y=4x-13\).

Answer

a) \(4\) b) \(y=4x-13\)
52640112
Find the first derivative of each function. 1) \(y=\frac{1}{4}x^4-2x^2+5\) 2) \(y=15-6x\) 3) \(z=4t^3-5t^2\) 4) \(f(x)=\frac{2x^3-9x}{3}\) 5) \(y=ax^2+bx+c\), where \(a\), \(b\), and \(c\) are constants

Hints

- Use the power rule and constant-multiple rule. - What is the derivative of a term with no variable? - You can distribute division across the terms in a numerator. - Differentiate with respect to the variable used in each function.

Solution

1. Differentiate the first function term by term: \(y'=x^3-4x\). 2. The derivative of \(15\) is \(0\), so \(y'=-6\). 3. Differentiate with respect to \(t\): \(z'=12t^2-10t\). 4. Rewrite \(f(x)=\frac{2}{3}x^3-3x\). Then \(f'(x)=2x^2-3\). 5. Treat \(a\), \(b\), and \(c\) as constants: \(y'=2ax+b\).

Answer

1) \(y'=x^3-4x\) 2) \(y'=-6\) 3) \(z'=12t^2-10t\) 4) \(f'(x)=2x^2-3\) 5) \(y'=2ax+b\)
52747912
For \(x>0\), let \(f(x)=4\sqrt[5]{x^3}-1.2x^{-\frac{2}{5}}\). Find \(f'(x)\).

Hints

- Rewrite the fifth root as a power with a rational exponent. - Apply the power rule to each term. - It is often easier to put every term in the form \(ax^r\) before differentiating.

Solution

1. Rewrite \(\sqrt[5]{x^3}=x^{\frac{3}{5}}\), so \(f(x)=4x^{\frac{3}{5}}-1.2x^{-\frac{2}{5}}\). 2. Apply the power rule: \(f'(x)=4\left(\frac{3}{5}\right)x^{-\frac{2}{5}}-1.2\left(-\frac{2}{5}\right)x^{-\frac{7}{5}}=2.4x^{-\frac{2}{5}}+0.48x^{-\frac{7}{5}}\).

Answer

\(f'(x)=2.4x^{-\frac{2}{5}}+0.48x^{-\frac{7}{5}}\)
52748012
For \(x>0\), let \(f(x)=\frac{6x}{\sqrt[3]{x^2}}\). Find \(f'(x)\).

Hints

- Use the quotient of powers property to simplify the function first. - Rewrite \(\frac{x^a}{x^b}\) as \(x^{a-b}\). - Apply the power rule after simplifying.

Solution

1. Simplify with exponent rules: \(f(x)=\frac{6x}{x^{\frac{2}{3}}}=6x^{\frac{1}{3}}\). 2. Apply the power rule: \(f'(x)=6\left(\frac{1}{3}\right)x^{-\frac{2}{3}}=2x^{-\frac{2}{3}}\).

Answer

\(f'(x)=2x^{-\frac{2}{3}}=\frac{2}{\sqrt[3]{x^2}}\)
52885312
The point \(P=(2,2)\) lies on a power function of the form \(f(x)=ax^3\). a) Find \(a\). b) Verify that the tangent line at \(P\) has slope \(3\), and find its equation. c) Find the tangent line's x-intercept.

Hints

- Substitute the given point into the function to find the parameter. - Differentiate the power function after finding the parameter. - A point and slope determine a line. - An x-intercept has y-coordinate \(0\). - Solve the line equation after setting \(y=0\).

Solution

1. Substitute \((2,2)\) into \(f(x)=ax^3\): \(2=8a\), so \(a=\frac{1}{4}\). 2. Differentiate: \(f'(x)=3ax^2\). With \(a=\frac{1}{4}\), \(f'(2)=3\), so the tangent slope is \(3\). 3. A line with slope \(3\) through \((2,2)\) satisfies \(y-2=3(x-2)\). Thus, \(y=3x-4\). 4. At the x-intercept, \(y=0\). Solve \(0=3x-4\), giving \(x=\frac{4}{3}\). The intercept is \((\frac{4}{3},0)\).

Answer

a) \(a=\frac{1}{4}\) b) \(f'(2)=3\), and \(y=3x-4\) c) \((\frac{4}{3},0)\)
52888912
Let \(f(x)=x^3-2x^2\). Find an equation of the tangent line at each input. a) \(x=2\) b) \(x=1\)

Hints

- Use the derivative to find each tangent slope. - Find the corresponding point on the graph. - Use point-slope form for each tangent line. - The tangent slope equals the derivative at the input.

Solution

1. Differentiate: \(f'(x)=3x^2-4x\). 2. At \(x=2\), \(f(2)=0\) and \(f'(2)=4\). The tangent line is \(y=4(x-2)=4x-8\). 3. At \(x=1\), \(f(1)=-1\) and \(f'(1)=-1\). The tangent line is \(y+1=-(x-1)\), so \(y=-x\).

Answer

a) \(y=4x-8\) b) \(y=-x\)
52890112
Let \(f(x)=2x^2-5x\). Find the equation of the tangent line \(t_a\) at \(P=(a,f(a))\) in terms of \(a\).

Hints

- Write the general tangent line at \(x=a\). - The derivative gives the slope in terms of \(a\). - Evaluate the original function at \(a\). - Expand and combine like terms.

Solution

1. Differentiate: \(f'(x)=4x-5\). 2. At \(x=a\), the tangent slope is \(f'(a)=4a-5\), and the point is \((a,2a^2-5a)\). 3. Use point-slope form: \(y=(4a-5)(x-a)+2a^2-5a\). 4. Expand and simplify: \(y=(4a-5)x-4a^2+5a+2a^2-5a=(4a-5)x-2a^2\).

Answer

\(t_a: y=(4a-5)x-2a^2\)
52891512
Let \(f(x)=\frac{1}{8}x^2\). 1. Find an equation of the tangent line at \(x=4\). 2. Find the angle the tangent line makes with the positive x-axis, assuming equal scales on the coordinate axes.

Hints

- The derivative at \(x=4\) gives the tangent slope. - Use point-slope form for the line. - Relate slope and angle using tangent.

Solution

1. Find the point of tangency: \(f(4)=2\), so the point is \((4,2)\). 2. Differentiate: \(f'(x)=\frac{1}{4}x\). Thus, \(f'(4)=1\). 3. Write the tangent line: \(y-2=x-4\), so \(y=x-2\). 4. Since \(\tan(\alpha)=1\), the angle is \(\alpha=45^\circ\).

Answer

1. \(y=x-2\) 2. \(45^\circ\)
52896112
a) Find the derivatives of \(f_1(x)=x^3\), \(f_2(x)=x^5\), and \(f_3(x)=x^7\). b) Use the pattern to state a general derivative rule for \(f(x)=x^n\), where \(n\in\mathbb{N}\) and \(n\geq1\). c) A function \(h\) satisfies \(h'(x)=12x^{11}\). Give one possible formula for \(h(x)\).

Hints

- Compare how each exponent changes and what coefficient appears. - Look for a rule connecting the original exponent to the new coefficient and exponent. - To reverse the derivative in part c), which original exponent would produce \(x^{11}\)?

Solution

1. Apply the power rule: \(f_1'(x)=3x^2\), \(f_2'(x)=5x^4\), and \(f_3'(x)=7x^6\). 2. The pattern is \(\frac{d}{dx}(x^n)=nx^{n-1}\). 3. To reverse the power rule in part c), increase the exponent from \(11\) to \(12\) and divide the coefficient by \(12\). One possible function is \(h(x)=x^{12}\). More generally, \(h(x)=x^{12}+C\).

Answer

a) \(f_1'(x)=3x^2\), \(f_2'(x)=5x^4\), and \(f_3'(x)=7x^6\) b) \(\frac{d}{dx}(x^n)=nx^{n-1}\) c) One possible function is \(h(x)=x^{12}\).
52896512
Find each derivative. Write answers without negative exponents when possible. a) \(f(x)=x^{13}\) b) \(g(x)=\frac{1}{x^5}\), where \(x\neq0\) c) \(h(x)=x^{-9}\), where \(x\neq0\) d) \(s(t)=t^2t^{-6}\), where \(t\neq0\)

Hints

- Rewrite variables in denominators using negative exponents. - Use exponent rules to simplify products with the same base. - Apply the power rule by multiplying by the exponent and subtracting \(1\) from it.

Solution

1. For part a), the power rule gives \(f'(x)=13x^{12}\). 2. Rewrite part b) as \(g(x)=x^{-5}\). Then \(g'(x)=-5x^{-6}=-\frac{5}{x^6}\). 3. For part c), \(h'(x)=-9x^{-10}=-\frac{9}{x^{10}}\). 4. Simplify part d): \(s(t)=t^{-4}\). Then \(s'(t)=-4t^{-5}=-\frac{4}{t^5}\).

Answer

a) \(f'(x)=13x^{12}\) b) \(g'(x)=-\frac{5}{x^6}\), where \(x\neq0\) c) \(h'(x)=-\frac{9}{x^{10}}\), where \(x\neq0\) d) \(s'(t)=-\frac{4}{t^5}\), where \(t\neq0\)
52896812
The tangent line to \(f(x)=\frac{1}{4}x^4-x^2\) touches the graph at \(P=(-2,y)\). Find the equation of the tangent line.

Hints

- First find the complete point of tangency. - Use the power rule to find the derivative. - Evaluate the derivative at \(x=-2\). - Use point-slope form for the tangent line.

Solution

1. Find the point of tangency: \(f(-2)=\frac{1}{4}(-2)^4-(-2)^2=0\), so \(P=(-2,0)\). 2. Differentiate: \(f'(x)=x^3-2x\). 3. Find the slope: \(f'(-2)=-8+4=-4\). 4. Use point-slope form: \(y=-4(x+2)\), so \(y=-4x-8\).

Answer

\(y=-4x-8\)
52897512
Use the constant-multiple and power rules to find each derivative. a) \(f(x)=2.5x^4\) b) \(f(x)=\frac{5}{12}x^6\) c) \(f(x)=-\frac{3}{x^2}\), where \(x\neq0\) d) \(f(x)=6\sqrt{x}\), where \(x>0\)

Hints

- Rewrite reciprocals and radicals using negative or rational exponents. - A constant factor remains when differentiating. - Apply \(\frac{d}{dx}(x^n)=nx^{n-1}\).

Solution

1. For part a), \(f'(x)=2.5(4x^3)=10x^3\). 2. For part b), \(f'(x)=\frac{5}{12}(6x^5)=\frac{5}{2}x^5\). 3. Rewrite part c) as \(f(x)=-3x^{-2}\). Then \(f'(x)=6x^{-3}=\frac{6}{x^3}\). 4. Rewrite part d) as \(f(x)=6x^{1/2}\). Then \(f'(x)=3x^{-1/2}=\frac{3}{\sqrt{x}}\).

Answer

a) \(f'(x)=10x^3\) b) \(f'(x)=\frac{5}{2}x^5\) c) \(f'(x)=\frac{6}{x^3}\), where \(x\neq0\) d) \(f'(x)=\frac{3}{\sqrt{x}}\), where \(x>0\)
52898312
Find the derivative of \(f(x)=4x^6-\frac{1}{2}x^4+3x-5\) using the power, constant-multiple, and sum rules.

Hints

- Differentiate a sum one term at a time. - Keep constant coefficients when applying the power rule. - What is the derivative of a constant? - Recall that \(x=x^1\).

Solution

1. Differentiate \(4x^6\) to get \(24x^5\). 2. Differentiate \(-\frac{1}{2}x^4\) to get \(-2x^3\). 3. The derivative of \(3x\) is \(3\), and the derivative of \(-5\) is \(0\). 4. Therefore, \(f'(x)=24x^5-2x^3+3\).

Answer

\(f'(x)=24x^5-2x^3+3\)
52898712
Find the first derivative of \(f(x)=\frac{5}{6}x^6-1.2x^5+\sqrt{7}x^2-9\).

Hints

- Track how each exponent and coefficient changes under the power rule. - A term with no \(x\) has derivative \(0\). - Differentiate the function one term at a time. - Keep constant coefficients, including radicals, when differentiating.

Solution

1. Differentiate term by term using the power and constant-multiple rules. 2. The derivative is \(f'(x)=5x^5-6x^4+2\sqrt{7}x\).

Answer

\(f'(x)=5x^5-6x^4+2\sqrt{7}x\)
52898812
Find the first derivative of \(f(x)=\frac{1}{4}x^8-\frac{2}{3}x^6+\frac{3}{4}x^4-\sqrt[5]{10}x+\pi\).

Hints

- Radicals and \(\pi\) are constants with respect to \(x\). - What is the derivative of a term of the form \(cx\)? - Differentiate a sum term by term. - Decrease each power exponent by exactly \(1\).

Solution

1. Differentiate each term using the power, constant-multiple, and sum rules. 2. The polynomial terms give \(2x^7-4x^5+3x^3\). 3. The derivative of \(-\sqrt[5]{10}x\) is \(-\sqrt[5]{10}\), and the derivative of \(\pi\) is \(0\). 4. Therefore, \(f'(x)=2x^7-4x^5+3x^3-\sqrt[5]{10}\).

Answer

\(f'(x)=2x^7-4x^5+3x^3-\sqrt[5]{10}\)
52899712
Let \(f(x)=x^2-5x+2\). Find the point on the graph where the tangent line makes an angle of \(135^\circ\), measured counterclockwise from the positive x-axis.

Hints

- Convert the angle to a slope using tangent. - Set the derivative equal to that slope. - Find the y-coordinate after solving for the x-coordinate. - A point requires both coordinates.

Solution

1. An angle of \(135^\circ\) corresponds to slope \(\tan(135^\circ)=-1\). 2. Differentiate: \(f'(x)=2x-5\). 3. Set the derivative equal to the required slope: \(2x-5=-1\). Thus, \(x=2\). 4. Evaluate the function: \(f(2)=4-10+2=-4\). Therefore, the point is \((2,-4)\).

Answer

\((2,-4)\)
52900112
Find the first derivative of each function. Simplify each expression as much as possible before differentiating. a) \(f(x)=(x^2+5)(4x-3)\) b) \(h(t)=2t(t+4)-(t-1)^2\) c) \(g(z)=\frac{1}{5}(z^3-10z)+(z+2)(z-2)\)

Hints

- Expand products into sums of powers before differentiating. - Distribute a negative sign carefully across parentheses. - Use binomial identities when helpful. - After simplifying, differentiate each term with the power rule.

Solution

1. Expand part a): \(f(x)=4x^3-3x^2+20x-15\). Then \(f'(x)=12x^2-6x+20\). 2. Simplify part b): \(h(t)=2t^2+8t-(t^2-2t+1)=t^2+10t-1\). Then \(h'(t)=2t+10\). 3. Simplify part c): \(g(z)=\frac{1}{5}z^3-2z+z^2-4\). Then \(g'(z)=\frac{3}{5}z^2+2z-2\).

Answer

a) \(f'(x)=12x^2-6x+20\) b) \(h'(t)=2t+10\) c) \(g'(z)=\frac{3}{5}z^2+2z-2\)
52900212
Differentiate each function with respect to its variable. The letters \(a\), \(b\), and \(k\) are constant parameters. a) \(f(x)=k(x+a)^2-bx\) b) \(s(t)=(t^2+4)(t^2-4)+\frac{2}{3}t^3\) c) \(q(r)=3r(r-2)^2\)

Hints

- Treat parameters as constants. - Use a difference-of-squares identity in part b). - Expand the squared binomial in part c) before multiplying. - Distinguish the variable from constant factors in each term.

Solution

1. Expand part a): \(f(x)=kx^2+2akx+ka^2-bx\). Therefore, \(f'(x)=2kx+2ak-b\). 2. Use the difference of squares in part b): \((t^2+4)(t^2-4)=t^4-16\). Thus \(s(t)=t^4+\frac{2}{3}t^3-16\), and \(s'(t)=4t^3+2t^2\). 3. Expand part c): \(q(r)=3r^3-12r^2+12r\). Therefore, \(q'(r)=9r^2-24r+12\).

Answer

a) \(f'(x)=2kx+2ak-b\) b) \(s'(t)=4t^3+2t^2\) c) \(q'(r)=9r^2-24r+12\)
52903512
Find the first derivative of each function. a) \(f(x)=0.2x^5-2x^3+4x-1\) b) \(f(x)=\frac{4}{x}+6\sqrt{x}\), for \(x>0\) c) \(f(x)=cx^n+a\), where \(a,c\in\mathbb{R}\) and \(n\in\mathbb{N}\) with \(n\geq1\)

Hints

- Rewrite reciprocals and radicals as powers before differentiating. - A constant term has derivative \(0\). - Differentiate a sum term by term. - Treat parameters as constants with respect to \(x\).

Solution

1. Differentiate each term in part a): \(f'(x)=0.2\cdot5x^4-2\cdot3x^2+4=x^4-6x^2+4\). 2. For part b), rewrite \(f(x)=4x^{-1}+6x^{1/2}\). Then \(f'(x)=-4x^{-2}+3x^{-1/2}=-\frac{4}{x^2}+\frac{3}{\sqrt{x}}\), for \(x>0\). 3. For part c), treat \(a\), \(c\), and \(n\) as constants. The power rule gives \(f'(x)=ncx^{n-1}\).

Answer

a) \(f'(x)=x^4-6x^2+4\) b) \(f'(x)=-\frac{4}{x^2}+\frac{3}{\sqrt{x}}\), for \(x>0\) c) \(f'(x)=ncx^{n-1}\)
52903912
Let \(f(x)=0.25x^4-2x^2+5\). Find an equation of the tangent line at \(x=1\).

Hints

- A tangent line requires a point and a slope. - Use the derivative to find the slope at \(x=1\). - Evaluate the original function to find the point. - Use point-slope form.

Solution

1. Find the point of tangency: \(f(1)=0.25-2+5=3.25\), so the point is \((1,3.25)\). 2. Differentiate: \(f'(x)=x^3-4x\). 3. Find the slope: \(f'(1)=1-4=-3\). 4. Use point-slope form: \(y-3.25=-3(x-1)\), so \(y=-3x+6.25\).

Answer

\(y=-3x+6.25\)
53372712
Find the angle of inclination \(\alpha\) of the tangent line to \(f(x)=0.5x^2+1\) at \(x=1\).
Figure for problem 533727

Hints

- How are a line's slope and its angle of inclination related? - First find the tangent slope at the given input. - Use an inverse trigonometric function.

Solution

1. Differentiate: \(f'(x)=x\). 2. The tangent slope at \(x=1\) is \(m=f'(1)=1\). 3. Since \(m=\tan(\alpha)\), \(\alpha=\arctan(1)=45^\circ\).

Answer

\(\alpha=45^\circ\)
53372812
Find the angle of inclination of the tangent line to \(f(x)=4-x^2\) at \(x=0.5\).
Figure for problem 533728

Hints

- A line with negative slope has an angle of inclination between \(90^\circ\) and \(180^\circ\). - Convert a negative inverse-tangent result to the standard inclination interval by adding \(180^\circ\).

Solution

1. Differentiate: \(f'(x)=-2x\). 2. At \(x=0.5\), the slope is \(m=f'(0.5)=-1\). 3. The calculator value \(\arctan(-1)=-45^\circ\) is coterminal with an angle of inclination of \(135^\circ\) in the interval \([0^\circ,180^\circ)\).

Answer

\(135^\circ\)
53374812
Let \(f(x)=\frac{1}{x}+x\) for \(x>0\). Verify algebraically that the graph has a horizontal tangent at \(x_0=1\), and find the coordinates of the point of tangency.
Figure for problem 533748

Hints

- A horizontal tangent has slope \(0\). - Rewrite \(\frac{1}{x}\) using a negative exponent before differentiating. - Use the original function to find the y-coordinate.

Solution

1. Rewrite \(f(x)=x^{-1}+x\). By the power rule, \(f^{\prime}(x)=-x^{-2}+1=-\frac{1}{x^2}+1\). 2. Evaluate the derivative: \(f^{\prime}(1)=-1+1=0\), so the tangent is horizontal. 3. Evaluate the original function: \(f(1)=1+1=2\). The point of tangency is \((1, 2)\).

Answer

\(f^{\prime}(x)=-\frac{1}{x^2}+1\), \(f^{\prime}(1)=0\), and the point of tangency is \((1, 2)\).
53387112
Let \(f(x)=0.5x^2-2x+1\). Find an equation of the tangent line \(t\) to the graph of \(f\) at \(x_0=3\).
Figure for problem 533871

Hints

- Evaluate the function to find the point on the graph. - The derivative value is the tangent slope. - Use point-slope form or slope-intercept form.

Solution

1. Find the point of tangency: \(f(3)=0.5\cdot3^2-2\cdot3+1=-0.5\), so the point is \((3,-0.5)\). 2. Differentiate: \(f'(x)=x-2\). The tangent slope is \(f'(3)=1\). 3. Use point-slope form: \(y+0.5=x-3\), so \(y=x-3.5\).

Answer

\(t: y=x-3.5\)
53489312
Given \(f(x) = \frac{8}{x}\) for \(x > 0\), the line \(g\) has equation \(y = -2x + 12\). a) Show algebraically that the tangent line \(t\) to the graph of \(f\) at \(P(2, f(2))\) is parallel to \(g\). b) Find the equation of the tangent line \(t\).
Figure for problem 534893

Hints

- How is the slope of a tangent line related to the derivative? - When are two lines parallel? - What information do you need to write an equation of a line? - Recall the tangent-line formula at \(x=a\).

Solution

1. Rewrite \(f(x) = 8x^{-1}\) and differentiate: \(f'(x) = -8x^{-2} = -\frac{8}{x^2}\). 2. At \(x = 2\), the tangent slope is \(f'(2) = -\frac{8}{2^2} = -2\). 3. The slope of \(g\) is also \(-2\), so the tangent line and \(g\) are parallel. 4. Find the point of tangency: \(f(2) = \frac{8}{2} = 4\), so \(P=(2, 4)\). 5. Use point-slope form: \(y - 4 = -2(x - 2)\). Therefore, \(t: y = -2x + 8\).

Answer

a) Since \(f'(2) = -2\), the tangent line has the same slope as \(g\), so the lines are parallel. b) \(t: y = -2x + 8\)
52222412
Let \(g(x)=\frac{1}{2}x^2-3x\). a) Find the derivative function \(g'\). b) Find the point \(B=(b,g(b))\) where the tangent to the graph of \(g\) is parallel to the line \(y=2x+1\). c) Find an equation of that tangent line.

Hints

- What must be true about the slopes of parallel lines? - Read the slope of the given line from its equation. - Use the slope and point of tangency to write the tangent line equation.

Solution

1. Differentiate: \(g'(x)=x-3\). 2. Parallel lines have equal slopes. The given line has slope \(2\), so solve \(g'(b)=2\): \(b-3=2\), giving \(b=5\). 3. Evaluate the function: \(g(5)=\frac{1}{2}\cdot 5^2-3\cdot 5=-2.5\). Thus, \(B=(5,-2.5)\). 4. Use slope \(2\) and point \((5,-2.5)\): \(y+2.5=2(x-5)\). 5. Simplify: \(y=2x-12.5\).

Answer

a) \(g'(x)=x-3\) b) \(B=(5,-2.5)\) c) \(y=2x-12.5\)
52222512
Let \(f(x)=x^3-12x+5\), with derivative \(f'(x)=3x^2-12\). a) Find the slope of the graph at \(x=-1\) and at \(x=3\). b) Find all values of \(x\) where the slope of the graph is \(15\). c) Find the points on the graph where the tangent line is parallel to \(y=-9x+2\). d) Find an equation of the tangent line to the graph at \(S=(0,f(0))\).

Hints

- Evaluate the derivative to find a slope at a specified input. - Set the derivative equal to the required slope and solve. - Parallel lines have equal slopes. - To find a point on the graph, substitute its x-coordinate into the original function.

Solution

1. Evaluate the derivative: \(f'(-1)=3(-1)^2-12=-9\) and \(f'(3)=3(3)^2-12=15\). 2. For slope \(15\), solve \(3x^2-12=15\). Then \(x^2=9\), so \(x=-3\) or \(x=3\). 3. A line parallel to \(y=-9x+2\) must have slope \(-9\). Solve \(3x^2-12=-9\), which gives \(x^2=1\), so \(x=-1\) or \(x=1\). 4. Evaluate the function: \(f(-1)=16\) and \(f(1)=-6\). The points are \((-1,16)\) and \((1,-6)\). 5. At \(x=0\), \(f(0)=5\) and \(f'(0)=-12\). The tangent line is \(y-5=-12(x-0)\), or \(y=-12x+5\).

Answer

a) \(f'(-1)=-9\) and \(f'(3)=15\) b) \(x=-3\) and \(x=3\) c) \((-1,16)\) and \((1,-6)\) d) \(y=-12x+5\)
52222612
Let \(g(x)=\frac{1}{3}x^3+x^2-3x\), with derivative \(g'(x)=x^2+2x-3\). a) Find \(g'(-2)\) and \(g'(1)\). b) Find all values of \(x\) where the graph of \(g\) has slope \(5\). c) Find the points on the graph where the tangent line is parallel to \(y=-3x+10\).

Hints

- Evaluate the derivative to find the slope at a specified input. - Set the derivative equal to the required slope and solve the resulting equation. - Read the slope of a line from its equation. - Substitute each x-coordinate into the original function to find the corresponding point.

Solution

1. Evaluate the derivative: \(g'(-2)=(-2)^2+2(-2)-3=-3\) and \(g'(1)=1^2+2(1)-3=0\). 2. For slope \(5\), solve \(x^2+2x-3=5\). Factoring \(x^2+2x-8=(x+4)(x-2)\) gives \(x=-4\) or \(x=2\). 3. A tangent parallel to \(y=-3x+10\) must have slope \(-3\). Solve \(x^2+2x-3=-3\), or \(x(x+2)=0\). Thus, \(x=0\) or \(x=-2\). 4. Evaluate the function: \(g(0)=0\) and \(g(-2)=\frac{22}{3}\). Therefore, the points are \((0,0)\) and \((-2,\frac{22}{3})\).

Answer

a) \(g'(-2)=-3\) and \(g'(1)=0\) b) \(x=-4\) and \(x=2\) c) \((0,0)\) and \((-2,\frac{22}{3})\)
52229312
Let \(f(x)=\frac{1}{2}x^2-2x+1\). Find the coordinates of the point where the tangent line at \(P=(3,f(3))\) intersects the x-axis.

Hints

- Find the point of tangency and the derivative at \(x=3\). - A line is determined by a point and its slope. - The derivative gives the tangent line's slope. - What is the y-coordinate of every point on the x-axis?

Solution

1. Find the point of tangency: \(f(3)=\frac{1}{2}\cdot 3^2-2\cdot 3+1=-0.5\), so \(P=(3,-0.5)\). 2. Differentiate: \(f'(x)=x-2\). 3. Find the tangent slope: \(f'(3)=1\). 4. Write the tangent line: \(y+0.5=x-3\), so \(y=x-3.5\). 5. At an x-intercept, \(y=0\). Solve \(0=x-3.5\) to get \(x=3.5\).

Answer

\((3.5,0)\)
52229412
The graph of \(g(x)=x^3-4x\) has a tangent line at \(x=1\). Find the coordinates of the point where this tangent line intersects the x-axis.

Hints

- First find the point where the tangent touches the graph. - Use the derivative to find the tangent slope. - Write the tangent line equation. - A point on the x-axis has y-coordinate \(0\).

Solution

1. Find the point of tangency: \(g(1)=1^3-4(1)=-3\), so the point is \((1,-3)\). 2. Differentiate: \(g'(x)=3x^2-4\). 3. Find the tangent slope: \(g'(1)=3(1)^2-4=-1\). 4. Write the tangent line: \(y+3=-(x-1)\), so \(y=-x-2\). 5. Set \(y=0\) to find the x-intercept: \(0=-x-2\), giving \(x=-2\).

Answer

\((-2,0)\)
52229812
The graph of \(f(x)=\frac{1}{4}x^2+x\) has a tangent line at \(x=x_0\) that makes an angle of \(135^\circ\), measured counterclockwise from the positive x-axis. Find \(x_0\).

Hints

- Find the slope of a line whose angle of inclination is \(135^\circ\). - Express the tangent slope at an unknown input using the derivative. - Set the derivative equal to the required slope and solve.

Solution

1. Convert the angle to a slope: \(m=\tan(135^\circ)=-1\). 2. Differentiate: \(f'(x)=\frac{1}{2}x+1\). 3. Set the derivative equal to the required slope: \(\frac{1}{2}x_0+1=-1\). 4. Solve: \(\frac{1}{2}x_0=-2\), so \(x_0=-4\).

Answer

\(x_0=-4\)
52230812
At a point \(B\) on the graph of \(f(x)=x^2-4x+2\), the tangent line makes an angle of \(135^\circ\), measured counterclockwise from the positive x-axis. Find the coordinates of \(B\) and an equation of the tangent line.

Hints

- Convert the given angle to a slope. - Set the derivative equal to that slope to find the x-coordinate. - Substitute the x-coordinate into the original function, then write the tangent line.

Solution

1. Convert the angle to a slope: \(m=\tan(135^\circ)=-1\). 2. Differentiate: \(f'(x)=2x-4\). 3. Set the derivative equal to the tangent slope: \(2x-4=-1\). Solving gives \(x=1.5\). 4. Find the y-coordinate: \(f(1.5)=(1.5)^2-4(1.5)+2=-1.75\). Thus, \(B=(1.5,-1.75)\). 5. Use point-slope form: \(y+1.75=-(x-1.5)\), so \(y=-x-0.25\).

Answer

\(B=(1.5,-1.75)\) and \(y=-x-0.25\)
52231712
Let \(f(x)=0.5x^2-2x\). Find the equations of the tangent line \(t\) and the normal line \(n\) at \(x_0=4\). Then find their angles of inclination, \(\alpha_t\) and \(\alpha_n\).

Hints

- Evaluate the function to find the point of tangency. - Use the derivative for the tangent slope. - The normal slope is the negative reciprocal of the tangent slope. - Use inverse tangent to find each angle of inclination.

Solution

1. Find the point: \(f(4)=0.5\cdot4^2-2\cdot4=0\), so the point is \((4,0)\). 2. Differentiate: \(f'(x)=x-2\). The tangent slope is \(m_t=f'(4)=2\). 3. The tangent line is \(y=2(x-4)=2x-8\). 4. The normal slope is \(m_n=-\frac{1}{2}\), so the normal line is \(y=-0.5(x-4)=-0.5x+2\). 5. The tangent angle is \(\alpha_t=\arctan(2)\approx63.43^\circ\). The normal angle is \(\alpha_n=\arctan(-0.5)+180^\circ\approx153.43^\circ\).

Answer

\(t: y=2x-8\) \(n: y=-0.5x+2\) \(\alpha_t\approx63.43^\circ\), \(\alpha_n\approx153.43^\circ\)
52233012
For \(k>0\), let \(f_k(x)=kx^2-4k\). The graph intersects the x-axis at \(P=(-2,0)\) and \(Q=(2,0)\). Tangent lines at \(P\) and \(Q\) intersect at \(S\). Find \(k\) so that triangle \(PQS\) has a right angle at \(S\).

Hints

- What relationship must the slopes of two perpendicular nonvertical lines satisfy? - Use the derivative to express the tangent slopes at the two intercepts. - Substitute those slopes into the perpendicularity condition. - Use the condition \(k>0\) when choosing the solution.

Solution

1. Differentiate: \(f_k'(x)=2kx\). 2. The tangent slopes are \(m_P=f_k'(-2)=-4k\) and \(m_Q=f_k'(2)=4k\). 3. A right angle at \(S\) means the two tangent lines are perpendicular, so their slopes satisfy \(m_Pm_Q=-1\). 4. Substitute: \((-4k)(4k)=-1\), so \(-16k^2=-1\) and \(k^2=\frac{1}{16}\). 5. Since \(k>0\), \(k=\frac{1}{4}\).

Answer

\(k=\frac{1}{4}\)
52233112
Let \(f(x)=\frac{1}{2}x^2-3x+1\). a) Find equations of the tangent line and the normal line to the graph at \(x=4\). b) Find the value of \(x\) where the graph has an angle of inclination of \(135^\circ\). c) Determine algebraically whether \(y=-x-1\) is tangent to the graph at \(x=2\).

Hints

- The tangent slope is the derivative at the point. - The slopes of a tangent and its normal are negative reciprocals when both are defined. - Convert an angle of inclination to a slope using tangent. - To verify a tangent line, check both the point and the slope.

Solution

1. Differentiate: \(f'(x)=x-3\). 2. At \(x=4\), \(f(4)=-3\) and \(f'(4)=1\). The tangent line is \(y+3=x-4\), or \(y=x-7\). The normal slope is \(-1\), so the normal line is \(y+3=-(x-4)\), or \(y=-x+1\). 3. An angle of \(135^\circ\) corresponds to slope \(\tan(135^\circ)=-1\). Solve \(x-3=-1\) to get \(x=2\). 4. At \(x=2\), \(f(2)=-3\) and \(f'(2)=-1\). The tangent line is \(y+3=-(x-2)\), which simplifies to \(y=-x-1\). Therefore, the given line is tangent at \(x=2\).

Answer

a) Tangent: \(y=x-7\); normal: \(y=-x+1\) b) \(x=2\) c) Yes. At \(x=2\), the point is \((2,-3)\) and the tangent slope is \(-1\), giving \(y=-x-1\).
52233212
Let \(f(x)=\frac{1}{3}x^3-x\). a) Find an equation of the tangent line at \(P=(2,f(2))\). b) Find all values of \(x\) where the tangent line is parallel to the x-axis. c) Find an equation of the normal line at \(x=0\).

Hints

- A line parallel to the x-axis has slope \(0\). - Substitute the given input into the original function to find the point. - A normal line has slope equal to the negative reciprocal of the tangent slope. - Use point-slope form to write each line.

Solution

1. Differentiate: \(f'(x)=x^2-1\). 2. At \(x=2\), \(f(2)=\frac{2}{3}\) and \(f'(2)=3\). The tangent line is \(y-\frac{2}{3}=3(x-2)\), or \(y=3x-\frac{16}{3}\). 3. A tangent parallel to the x-axis has slope \(0\). Solve \(x^2-1=0\), giving \(x=-1\) and \(x=1\). 4. At \(x=0\), \(f(0)=0\) and the tangent slope is \(-1\). The normal slope is \(1\), so the normal line is \(y=x\).

Answer

a) \(y=3x-\frac{16}{3}\) b) \(x=-1\) and \(x=1\) c) \(y=x\)
52236012
Let \(f(x)=\frac{1}{4}x^4-2x^2+5\). a) Find the slope of the graph at \(x=1\). b) Find an equation of the tangent line at \(P=(2,f(2))\). c) Find an equation of the normal line at \(x=-1\).

Hints

- The derivative gives the graph's slope at a point. - A tangent line with slope \(0\) is horizontal. - The normal slope is the negative reciprocal of the tangent slope. - Use point-slope form for each line.

Solution

1. Differentiate: \(f'(x)=x^3-4x\). 2. At \(x=1\), \(f'(1)=1-4=-3\). 3. At \(x=2\), \(f(2)=1\) and \(f'(2)=0\). The tangent line is horizontal, so its equation is \(y=1\). 4. At \(x=-1\), \(f(-1)=\frac{13}{4}\) and the tangent slope is \(f'(-1)=3\). The normal slope is \(-\frac{1}{3}\). 5. The normal line is \(y-\frac{13}{4}=-\frac{1}{3}(x+1)\), which simplifies to \(y=-\frac{1}{3}x+\frac{35}{12}\).

Answer

a) \(-3\) b) \(y=1\) c) \(y=-\frac{1}{3}x+\frac{35}{12}\)
52236412
Let \(f(x)=x^2-4x+5\). At an input \(x_0\), the normal line to the graph has slope \(m_n=0.5\). a) Find \(x_0\). b) Find the equation of this normal line.

Hints

- Convert the known normal slope to the tangent slope. - The derivative gives the tangent slope at each input. - Set the derivative equal to the required tangent slope. - Evaluate the function before writing the line equation.

Solution

1. The tangent slope is the negative reciprocal of the normal slope: \(m_t=-\frac{1}{0.5}=-2\). 2. Differentiate: \(f'(x)=2x-4\). Set \(f'(x_0)=-2\): \(2x_0-4=-2\), so \(x_0=1\). 3. Evaluate the function: \(f(1)=2\), so the point is \((1,2)\). 4. The normal line is \(y-2=0.5(x-1)\), or \(y=0.5x+1.5\).

Answer

a) \(x_0=1\) b) \(n: y=0.5x+1.5\)
52238212
Let \(p(x)=x^2-4x+6\). The normal line \(n\) to the parabola at \(A(3,3)\) intersects the line \(g: y=x-3\) at \(S\). Find the coordinates of \(S\).

Hints

- Find the tangent slope at \(A\) using the derivative. - Convert the tangent slope to the normal slope. - Write the normal line through \(A\). - Solve the two line equations as a system.

Solution

1. Differentiate: \(p'(x)=2x-4\). The tangent slope at \(x=3\) is \(p'(3)=2\). 2. The normal slope is \(-\frac{1}{2}\). 3. Through \(A(3,3)\), the normal line is \(y-3=-0.5(x-3)\), or \(y=-0.5x+4.5\). 4. Set the normal equation equal to \(y=x-3\): \(-0.5x+4.5=x-3\). Thus, \(7.5=1.5x\), so \(x=5\). 5. Then \(y=5-3=2\), so \(S=(5,2)\).

Answer

\(S=(5,2)\)
52238912
Let \(f(x)=\frac{1}{3}x^3-x^2-2x\). The graph has slope \(1\) at two points, \(P\) and \(Q\). Together with the origin \(O=(0,0)\), these points form a triangle. Find the area of triangle \(OPQ\).

Hints

- Set the derivative equal to the given slope. - Substitute each solution into the original function to find the points. - Use a coordinate-area formula for a triangle whose one vertex is the origin. - Take the absolute value so the area is positive.

Solution

1. Differentiate: \(f'(x)=x^2-2x-2\). 2. Set the derivative equal to \(1\): \(x^2-2x-2=1\), or \(x^2-2x-3=0\). Thus, \(x=-1\) or \(x=3\). 3. Find the corresponding points: \(f(-1)=\frac{2}{3}\) and \(f(3)=-6\). Thus, the points are \((-1,\frac{2}{3})\) and \((3,-6)\). 4. With one vertex at the origin, the area is \(\frac{1}{2}|x_1y_2-x_2y_1|\). 5. Therefore, \(A=\frac{1}{2}|(-1)(-6)-3(\frac{2}{3})|=\frac{1}{2}|6-2|=2\).

Answer

\(2\) square units
52240312
Let \(f(x)=x^3-3x^2-9x+11\). 1. Show that the tangent line to the graph at its y-intercept is \(y=-9x+11\). 2. Find the x-coordinates of the points where the tangent line is parallel to the x-axis. 3. Find the coordinates of \(P=(4,f(4))\) and an equation of the tangent line at \(P\).

Hints

- The y-intercept occurs where \(x=0\). - A horizontal tangent has derivative \(0\). - The derivative at a point gives the tangent slope. - Use point-slope form to write each tangent line.

Solution

1. The y-intercept occurs at \(x=0\), and \(f(0)=11\). Differentiate: \(f'(x)=3x^2-6x-9\), so \(f'(0)=-9\). The tangent line is \(y-11=-9(x-0)\), or \(y=-9x+11\). 2. A horizontal tangent has slope \(0\). Solve \(3x^2-6x-9=0\). Dividing by \(3\) gives \(x^2-2x-3=0\), so \(x=-1\) or \(x=3\). 3. At \(x=4\), \(f(4)=-9\) and \(f'(4)=15\). Thus, \(P=(4,-9)\), and the tangent line is \(y+9=15(x-4)\), or \(y=15x-69\).

Answer

1. At \(x=0\), \(f(0)=11\) and \(f'(0)=-9\), so the tangent is \(y=-9x+11\). 2. \(x=-1\) and \(x=3\) 3. \(P=(4,-9)\) and \(y=15x-69\)
52243512
Find an equation of the tangent line to \(f(x)=x^3-2x^2+1\) at \(P=(2,f(2))\). Also find the angle that the tangent line makes with the positive x-axis.

Hints

- Find the point of tangency from the original function. - Use the derivative to find the tangent slope. - Write the line using point-slope form. - Relate the slope to the angle using tangent.

Solution

1. Find the point of tangency: \(f(2)=2^3-2(2)^2+1=1\), so \(P=(2,1)\). 2. Differentiate: \(f'(x)=3x^2-4x\). 3. Find the slope: \(f'(2)=3(2)^2-4(2)=4\). 4. Write the tangent line: \(y-1=4(x-2)\), so \(y=4x-7\). 5. The angle \(\alpha\) satisfies \(\tan(\alpha)=4\), so \(\alpha=\arctan(4)\approx 75.96^\circ\).

Answer

Tangent line: \(y=4x-7\) Angle: \(75.96^\circ\), approximately
52243612
Let \(f(x)=-0.25x^4+x^2+1\). Find an equation of the tangent line at \(P=(1,f(1))\) and the angle that the graph makes with the positive x-axis at that point.

Hints

- Use the derivative to find the tangent slope. - Substitute \(x=1\) into the original function to find the point. - Relate the slope to the angle using tangent. - Write the line in slope-intercept or point-slope form.

Solution

1. Find the point of tangency: \(f(1)=-0.25(1)^4+1^2+1=1.75\), so \(P=(1,1.75)\). 2. Differentiate: \(f'(x)=-x^3+2x\). 3. Find the slope: \(f'(1)=1\). 4. Write the tangent line: \(y-1.75=x-1\), so \(y=x+0.75\). 5. Since \(\tan(\alpha)=1\), the angle is \(\alpha=45^\circ\).

Answer

Tangent line: \(y=x+0.75\) Angle: \(45^\circ\)
52260812
The graph of \(f(x)=\frac{1}{3}x^3-4x+2\) has two tangent lines parallel to \(y=5x-7\). Find equations of both tangent lines.

Hints

- Parallel lines have equal slopes. - Set the derivative equal to the specified slope. - Find the corresponding points on the graph. - Use each point and the common slope to write a tangent line.

Solution

1. Differentiate: \(f'(x)=x^2-4\). 2. The given line has slope \(5\). Set \(f'(x)=5\): \(x^2-4=5\), so \(x=-3\) or \(x=3\). 3. Evaluate the function: \(f(-3)=5\) and \(f(3)=-1\). 4. At \((-3,5)\), the tangent line is \(y-5=5(x+3)\), or \(y=5x+20\). 5. At \((3,-1)\), the tangent line is \(y+1=5(x-3)\), or \(y=5x-16\).

Answer

\(y=5x+20\) and \(y=5x-16\)
52280012
Consider the family \(g_k(x)=x^3-kx^2+4\), where \(k\in\mathbb{R}\). a) Find the derivative function \(g_k'\). b) Find \(k\) so that the graph has slope \(4\) at \(x=2\). c) For the value of \(k\) from part b, find an equation of the tangent line at \(x=2\).

Hints

- Treat the parameter as a constant when differentiating. - Set the derivative at \(x=2\) equal to the required slope. - Find the point of tangency using the corresponding function. - Use point-slope form for the tangent line.

Solution

1. Differentiate while treating \(k\) as a constant: \(g_k'(x)=3x^2-2kx\). 2. Require slope \(4\) at \(x=2\): \(3(2)^2-2k(2)=4\). Thus, \(12-4k=4\), so \(k=2\). 3. For \(k=2\), \(g_2(2)=2^3-2(2)^2+4=4\). The point of tangency is \((2,4)\). 4. Using slope \(4\), the tangent line is \(y-4=4(x-2)\), or \(y=4x-4\).

Answer

a) \(g_k'(x)=3x^2-2kx\) b) \(k=2\) c) \(y=4x-4\)
52292112
Let \(f(x)=0.5x^2-2x-1\). Find an equation of the tangent line at \(P=(-1,f(-1))\). Then find the coordinates of the tangent line's y-intercept.

Hints

- Use the derivative to find the tangent slope. - Find the complete point of tangency. - Use point-slope form to write the line. - Set \(x=0\) to find the y-intercept.

Solution

1. Differentiate: \(f'(x)=x-2\). 2. At \(x=-1\), \(f(-1)=1.5\) and \(f'(-1)=-3\). 3. Write the tangent line: \(y-1.5=-3(x+1)\), so \(y=-3x-1.5\). 4. At the y-intercept, \(x=0\). Thus, \(y=-1.5\), and the intercept is \((0,-1.5)\).

Answer

Tangent line: \(y=-3x-1.5\) Y-intercept: \((0,-1.5)\)
52292212
Let \(g(x)=\frac{1}{3}x^3-x^2+2\). a) Find the equation of the tangent line \(t\) at \(x_0=3\). b) Find the equation of the normal line \(n\) at \(Q(3,g(3))\).

Hints

- Evaluate the function to find the full point. - Use the derivative for the tangent slope. - Perpendicular line slopes are negative reciprocals. - Use point-slope form for both lines.

Solution

1. Differentiate: \(g'(x)=x^2-2x\). 2. Evaluate the function and derivative: \(g(3)=2\) and \(g'(3)=3\). 3. The tangent line is \(y-2=3(x-3)\), or \(y=3x-7\). 4. The normal slope is \(-\frac{1}{3}\). Thus, the normal line is \(y-2=-\frac{1}{3}(x-3)\), or \(y=-\frac{1}{3}x+3\).

Answer

a) \(t: y=3x-7\) b) \(n: y=-\frac{1}{3}x+3\)
52549012
Consider the family of functions \(g_a(x)=ax^3-4x^2+ax\), where \(a\in\mathbb{R}\). a) Find \(g_a'(x)\). b) Find the value of \(a\) for which the graph has a horizontal tangent at \(x=1\).

Hints

- What value must the derivative have at a horizontal tangent? - Treat \(a\) as a constant while differentiating with respect to \(x\). - Substitute the given x-coordinate into the derivative equation.

Solution

1. Treat \(a\) as a constant and apply the power rule: \(g_a'(x)=3ax^2-8x+a\). 2. A horizontal tangent at \(x=1\) requires \(g_a'(1)=0\). 3. Substitute \(x=1\): \(3a-8+a=0\). 4. Solve \(4a-8=0\) to obtain \(a=2\).

Answer

a) \(g_a'(x)=3ax^2-8x+a\) b) \(a=2\)
52596112
Consider the family of functions \(f_k(x)=x^3-kx^2+2x\), where \(k\in\mathbb{R}\). a) Find \(k\) so that the graph passes through \((2, 8)\). b) Find the slope of every graph at the origin. c) Find \(k\) so that the graph has slope \(11\) at \(x=3\).

Hints

- Substitute a point into the original function to find a parameter. - The derivative gives the slope at a specified x-value. - Apply the power rule term by term. - The origin has x-coordinate \(0\).

Solution

1. Substitute \((2, 8)\): \(8-4k+4=8\). Solving gives \(k=1\). 2. Differentiate: \(f_k'(x)=3x^2-2kx+2\). 3. At the origin, \(f_k'(0)=2\), independent of \(k\). 4. For slope \(11\) at \(x=3\), solve \(f_k'(3)=11\): \(27-6k+2=11\). 5. This gives \(6k=18\), so \(k=3\).

Answer

a) \(k=1\) b) The slope is \(2\). c) \(k=3\)
52596212
Consider the family of functions \(g_t(x)=x^3-3x^2+tx\), where \(t\in\mathbb{R}\). a) Find \(t\) so that \((1, 2)\) lies on the graph. b) Find the slope at the origin in terms of \(t\). c) Find \(t\) so that the tangent line at \(x=2\) has slope \(5\).

Hints

- Substitute the given point into the function. - Differentiate to find a slope formula. - Evaluate the derivative at the specified x-value. - Decide whether the requested slope is constant or depends on the parameter.

Solution

1. Substitute \((1, 2)\): \(1-3+t=2\), so \(t=4\). 2. Differentiate: \(g_t'(x)=3x^2-6x+t\). 3. At the origin, \(g_t'(0)=t\). 4. For slope \(5\) at \(x=2\), solve \(g_t'(2)=5\): \(12-12+t=5\). 5. Therefore, \(t=5\).

Answer

a) \(t=4\) b) The slope is \(t\). c) \(t=5\)
52639212
Let \(g(x)=\frac{1}{3}x^3-x\). 1. Find all points on the graph where the tangent line makes an angle of \(45^\circ\) with the positive x-axis. 2. Explain algebraically why no point on the graph has a tangent line with an angle of inclination of \(120^\circ\).

Hints

- Convert each angle to a slope using tangent. - Set the derivative equal to the required slope. - Check whether the resulting squared equation has real solutions. - Consider the range of \(g'(x)=x^2-1\).

Solution

1. An angle of \(45^\circ\) corresponds to slope \(\tan(45^\circ)=1\). Differentiate: \(g'(x)=x^2-1\). 2. Solve \(x^2-1=1\). Then \(x^2=2\), so \(x=\pm\sqrt{2}\). 3. Evaluate the function: \(g(\sqrt{2})=-\frac{\sqrt{2}}{3}\) and \(g(-\sqrt{2})=\frac{\sqrt{2}}{3}\). The points are \((\sqrt{2},-\frac{\sqrt{2}}{3})\) and \((-\sqrt{2},\frac{\sqrt{2}}{3})\). 4. An angle of \(120^\circ\) corresponds to slope \(\tan(120^\circ)=-\sqrt{3}\). The equation \(x^2-1=-\sqrt{3}\) becomes \(x^2=1-\sqrt{3}\). 5. Since \(1-\sqrt{3}<0\), there is no real solution. Equivalently, \(g'(x)=x^2-1\ge -1\), so it can never equal \(-\sqrt{3}\).

Answer

1. \((\sqrt{2},-\frac{\sqrt{2}}{3})\) and \((-\sqrt{2},\frac{\sqrt{2}}{3})\) 2. No such point exists because \(g'(x)\ge -1\), while \(\tan(120^\circ)=-\sqrt{3}<-1\).
52640012
Let \(g(x)=\frac{1}{3}x^3-2x^2+3x\). a) Find all values of \(x\) where the graph has a horizontal tangent line. b) Determine whether the graph is steeper at \(x=0\) or at \(x=4\).

Hints

- A horizontal tangent has slope \(0\). - Evaluate the derivative at both specified inputs. - Compare absolute values when comparing steepness.

Solution

1. Differentiate: \(g'(x)=x^2-4x+3\). 2. Horizontal tangent lines occur where \(g'(x)=0\). Factor \(x^2-4x+3=(x-1)(x-3)\), so \(x=1\) and \(x=3\). 3. Evaluate the slopes: \(g'(0)=3\) and \(g'(4)=3\). 4. Steepness is determined by the absolute value of slope. Since both slopes have magnitude \(3\), the graph is equally steep at the two points.

Answer

a) \(x=1\) and \(x=3\) b) The graph is equally steep at \(x=0\) and \(x=4\); the slope is \(3\) at each point.
52667212
For \(k\in\mathbb{R}\), let \(f_k(x)=x^4-kx^2+4\). Find the value of \(k\) for which the tangent line to the graph of \(f_k\) at \(x=1\) passes through \(Q(0, 1)\).

Hints

- Find the point and the derivative at \(x=1\) in terms of \(k\). - Write the tangent line in point-slope form. - Substitute the coordinates of \(Q\) into the tangent-line equation. - Solve the resulting equation for \(k\).

Solution

1. At \(x=1\), the point on the graph is \(B(1, f_k(1))=(1, 5-k)\). 2. Differentiate: \(f_k'(x)=4x^3-2kx\), so the tangent slope at \(x=1\) is \(4-2k\). 3. The tangent line is \(y-(5-k)=(4-2k)(x-1)\). 4. Because the line passes through \(Q(0, 1)\), \(1-(5-k)=(4-2k)(-1)\). 5. Simplifying gives \(k-4=-4+2k\), so \(k=0\).

Answer

\(k=0\)
52742312
Let \(f(x)=\frac{(3x-2)^2}{2x}\). a) Find an equation of the tangent line to the graph at \(P(1,0.5)\). b) Identify the vertical asymptote of \(f'\), and determine whether \(f'\) has the same sign on both sides of it.

Hints

- Simplify the rational expression before differentiating. - The derivative value gives the tangent slope. - Use point-slope form for the tangent line. - An even power in the denominator has the same sign on both sides of its zero.

Solution

1. Simplify before differentiating: \(f(x)=\frac{9x^2-12x+4}{2x}=4.5x-6+\frac{2}{x}\). 2. Differentiate: \(f'(x)=4.5-\frac{2}{x^2}=\frac{9x^2-4}{2x^2}\). 3. At \(x=1\), the slope is \(f'(1)=2.5\). Using point-slope form through \((1,0.5)\), \(y-0.5=2.5(x-1)\), so \(y=2.5x-2\). 4. The derivative is undefined at \(x=0\), while its numerator approaches \(-4\neq0\). Thus \(x=0\) is a vertical asymptote of \(f'\). Because the denominator contains \(x^2\), it is positive on both sides, so \(f'\) approaches \(-\infty\) from both sides and does not change sign across the asymptote.

Answer

a) \(y=2.5x-2\). b) The vertical asymptote of \(f'\) is \(x=0\). The derivative is negative on both sides near the asymptote, so there is no sign change.
52746712
Let \(f(x)=x^{\frac{1}{4}}\), with \(f'(x)=\frac{1}{4}x^{-\frac{3}{4}}\) for \(x>0\). 1. Find the derivative of \(g(x)=x^{\frac{5}{4}}\) by writing \(g(x)=x\cdot f(x)\) and applying the product rule. 2. Find the derivative of \(k(x)=x^{-\frac{1}{4}}\) by writing \(k(x)=\frac{1}{f(x)}\) and applying the quotient rule or another appropriate rule. 3. Compare your results with the power rule for integer exponents, \((x^n)'=nx^{n-1}\). State a conjecture for the derivative of \(x^r\), where \(r\in\mathbb{Q}\). Include the restrictions needed for real-valued functions.

Hints

- Recall the product rule: \((uv)'=u'v+uv'\). - Use the exponent rules \(x^a\cdot x^b=x^{a+b}\) and \(\frac{x^a}{x^b}=x^{a-b}\). - Compare the coefficient in each derivative with the original exponent. - Check whether the new exponent is exactly \(1\) less than the original exponent.

Solution

1. Using \(g(x)=x\cdot x^{\frac{1}{4}}\), the product rule gives \(g'(x)=x^{\frac{1}{4}}+x\cdot\frac{1}{4}x^{-\frac{3}{4}}=x^{\frac{1}{4}}+\frac{1}{4}x^{\frac{1}{4}}=\frac{5}{4}x^{\frac{1}{4}}\). 2. Using \(k(x)=\frac{1}{f(x)}\), \(k'(x)=\frac{-f'(x)}{(f(x))^2}=\frac{-\frac{1}{4}x^{-\frac{3}{4}}}{x^{\frac{1}{2}}}=-\frac{1}{4}x^{-\frac{5}{4}}\). 3. Both results have the form \((x^r)'=rx^{r-1}\). For a real-valued power function, the rule applies at points in its domain where the function is differentiable. In particular, it is valid for every rational \(r\) when \(x>0\).

Answer

1. \(g'(x)=\frac{5}{4}x^{\frac{1}{4}}\) 2. \(k'(x)=-\frac{1}{4}x^{-\frac{5}{4}}\) 3. \((x^r)'=rx^{r-1}\) wherever the real-valued function \(x^r\) is differentiable; in particular, for \(x>0\).
52746812
Find the slope of the tangent line to the graph of \(f\) at \(x=1\), where \(f(x)=\frac{3}{4}x\sqrt{x}-\frac{2}{\sqrt[4]{x}}\).

Hints

- Rewrite each radical and reciprocal as a power with a rational exponent. - The derivative evaluated at a point gives the slope of the tangent line there. - Any power of \(1\) equals \(1\). - Watch the signs when differentiating negative exponents.

Solution

1. Rewrite the function using rational exponents: \(f(x)=\frac{3}{4}x^{\frac{3}{2}}-2x^{-\frac{1}{4}}\). 2. Apply the power rule: \(f'(x)=\frac{3}{4}\cdot\frac{3}{2}x^{\frac{1}{2}}-2\left(-\frac{1}{4}\right)x^{-\frac{5}{4}}=\frac{9}{8}x^{\frac{1}{2}}+\frac{1}{2}x^{-\frac{5}{4}}\). 3. Evaluate at \(x=1\): \(f'(1)=\frac{9}{8}+\frac{1}{2}=\frac{13}{8}=1.625\).

Answer

The tangent line has slope \(\frac{13}{8}=1.625\).
52747312
For each function, find \(f'(x)\), and then evaluate \(f'(1)\). a) \(f(x)=1.2x^{\frac{1}{2}}\) b) \(f(x)=\sqrt[3]{x^7}\) c) \(f(x)=\frac{6}{\sqrt{x^3}}\)

Hints

- First rewrite radicals and reciprocals in the form \(x^r\). - Apply the power rule to each term. - When differentiating a power, multiply by the exponent and subtract \(1\) from the exponent. - Substituting \(x=1\) simplifies every power of \(1\) to \(1\).

Solution

1. a) By the power rule, \(f'(x)=1.2\left(\frac{1}{2}\right)x^{-\frac{1}{2}}=0.6x^{-\frac{1}{2}}\). Therefore, \(f'(1)=0.6\). 2. b) Rewrite \(f(x)=x^{\frac{7}{3}}\). Then \(f'(x)=\frac{7}{3}x^{\frac{4}{3}}\), so \(f'(1)=\frac{7}{3}\approx2.333\). 3. c) Rewrite \(f(x)=6x^{-\frac{3}{2}}\). Then \(f'(x)=-9x^{-\frac{5}{2}}\), so \(f'(1)=-9\).

Answer

a) \(f'(x)=0.6x^{-\frac{1}{2}}\); \(f'(1)=0.6\) b) \(f'(x)=\frac{7}{3}x^{\frac{4}{3}}\); \(f'(1)=\frac{7}{3}\approx2.333\) c) \(f'(x)=-9x^{-\frac{5}{2}}\); \(f'(1)=-9\)
52747412
For each function, find \(g'(x)\), and then find the slope of its graph at \(x=1\). a) \(g(x)=x^{\frac{7}{5}}\sqrt[5]{x^4}\) b) \(g(x)=\frac{5}{2}(\sqrt[4]{x})^{-3}\) c) \(g(x)=\frac{\sqrt[3]{x^2}}{x^2}\)

Hints

- Simplify each expression with exponent rules before differentiating. - Recall that \(\sqrt[n]{x^m}=x^{\frac{m}{n}}\). - A power in the denominator can be written with a negative exponent. - When multiplying powers with the same base, add their exponents.

Solution

1. a) Combine the powers: \(g(x)=x^{\frac{7}{5}}x^{\frac{4}{5}}=x^{\frac{11}{5}}\). Thus, \(g'(x)=\frac{11}{5}x^{\frac{6}{5}}\), and \(g'(1)=\frac{11}{5}=2.2\). 2. b) Rewrite \(g(x)=\frac{5}{2}x^{-\frac{3}{4}}\). Thus, \(g'(x)=-\frac{15}{8}x^{-\frac{7}{4}}\), and \(g'(1)=-\frac{15}{8}=-1.875\). 3. c) Rewrite \(g(x)=x^{\frac{2}{3}-2}=x^{-\frac{4}{3}}\). Thus, \(g'(x)=-\frac{4}{3}x^{-\frac{7}{3}}\), and \(g'(1)=-\frac{4}{3}\approx-1.333\).

Answer

a) \(g'(x)=\frac{11}{5}x^{\frac{6}{5}}\); \(g'(1)=\frac{11}{5}=2.2\) b) \(g'(x)=-\frac{15}{8}x^{-\frac{7}{4}}\); \(g'(1)=-\frac{15}{8}=-1.875\) c) \(g'(x)=-\frac{4}{3}x^{-\frac{7}{3}}\); \(g'(1)=-\frac{4}{3}\approx-1.333\)
52789712
Consider the family of functions \(f_{a,b}(x)=ax^2+bx+5\), where \(a,b\in\mathbb{R}\). The tangent line to the graph at \(P(2, 0)\) and the coordinate axes enclose a triangle in the first quadrant with area \(6\). Find \(a\) and \(b\).

Hints

- Use the fact that \(P\) lies on the graph. - The point \(P(2, 0)\) is also the tangent line's x-intercept. - Use the triangle's area to find the tangent line's y-intercept. - Find the tangent slope from the intercepts and match it to the derivative at \(x=2\).

Solution

1. Since \(P(2, 0)\) lies on the graph, \(f_{a,b}(2)=0\). Therefore, \(4a+2b+5=0\), or \(4a+2b=-5\). 2. The tangent line crosses the x-axis at \((2, 0)\). Let its y-intercept be \((0, y_0)\). The triangle's area is \(\frac{1}{2}\cdot2\cdot y_0=6\), so \(y_0=6\). 3. The tangent line through \((0, 6)\) and \((2, 0)\) has slope \(\frac{0-6}{2-0}=-3\). 4. Differentiate: \(f_{a,b}'(x)=2ax+b\). At \(x=2\), the tangent slope gives \(4a+b=-3\). 5. Solve the system \(4a+2b=-5\) and \(4a+b=-3\). Subtraction gives \(b=-2\), and then \(a=-\frac{1}{4}\).

Answer

\(a=-\frac{1}{4}\) and \(b=-2\)
52885412
Let \(f(x)=x^2-4x+5\). a) Find the vertex of the graph. b) Verify whether \(P=(3,2)\) lies on the graph. c) Verify that the tangent line at \(P\) has slope \(2\). Find its equation and determine whether it passes through the origin.

Hints

- Rewrite the quadratic in vertex form. - Substitute the point's x-coordinate into the function. - Use the derivative to verify the tangent slope at \(P\). - Use the point and slope to write the tangent line. - Test the origin by substituting \((0,0)\) into the line equation.

Solution

1. Complete the square: \(f(x)=(x-2)^2+1\). Therefore, the vertex is \((2,1)\). 2. Evaluate the function: \(f(3)=9-12+5=2\). Thus, \(P=(3,2)\) lies on the graph. 3. Differentiate: \(f'(x)=2x-4\). Then \(f'(3)=2\), so the tangent slope at \(P\) is \(2\). 4. A line with slope \(2\) through \((3,2)\) satisfies \(y-2=2(x-3)\), so \(y=2x-4\). 5. At \(x=0\), the line has value \(-4\), not \(0\). Therefore, it does not pass through the origin.

Answer

a) \((2,1)\) b) Yes, because \(f(3)=2\). c) \(f'(3)=2\), so the tangent line is \(y=2x-4\); it does not pass through the origin.
52889012
Let \(f(x)=\frac{1}{2}x^2+2\). Find the equations of the tangent line \(t\) and the normal line \(n\) at \(P(2,f(2))\).

Hints

- Evaluate the function to find the full point. - The derivative value gives the tangent slope. - The normal slope is the negative reciprocal of the tangent slope. - Use point-slope form.

Solution

1. Find the point: \(f(2)=\frac{1}{2}\cdot2^2+2=4\), so \(P=(2,4)\). 2. Differentiate: \(f'(x)=x\). The tangent slope is \(f'(2)=2\). 3. The tangent line is \(y-4=2(x-2)\), or \(y=2x\). 4. The normal slope is \(-\frac{1}{2}\). Thus, \(y-4=-\frac{1}{2}(x-2)\), or \(y=-\frac{1}{2}x+5\).

Answer

\(t: y=2x\) \(n: y=-\frac{1}{2}x+5\)
52889312
Let \(f(x)=x^3-3x\). a) Find an equation of the tangent line at \(P=(2,f(2))\). b) Find all values of \(x\) where the graph has a horizontal tangent line. c) Show that the tangent line at an arbitrary input \(u\) has equation \(y=(3u^2-3)x-2u^3\).

Hints

- The derivative gives the tangent slope. - A horizontal tangent has slope \(0\). - Write the general tangent line at \(x=u\). - Expand and combine like terms carefully.

Solution

1. Differentiate: \(f'(x)=3x^2-3\). 2. At \(x=2\), \(f(2)=2\) and \(f'(2)=9\). Thus, \(y-2=9(x-2)\), so \(y=9x-16\). 3. A horizontal tangent has slope \(0\). Solve \(3x^2-3=0\), giving \(x=-1\) and \(x=1\). 4. At an arbitrary input \(u\), the point is \((u,u^3-3u)\) and the slope is \(3u^2-3\). 5. Substitute into point-slope form: \(y=(3u^2-3)(x-u)+u^3-3u\). Expanding gives \(y=(3u^2-3)x-2u^3\).

Answer

a) \(y=9x-16\) b) \(x=-1\) and \(x=1\) c) Substituting \(f(u)=u^3-3u\) and \(f'(u)=3u^2-3\) into point-slope form simplifies to \(y=(3u^2-3)x-2u^3\).
52889412
Let \(f(x)=\frac{1}{2}x^2-2\). a) Find equations of the tangent line and the normal line at \(B=(2,f(2))\). b) The tangent line and the coordinate axes form a triangle. Find its area.

Hints

- The normal slope is the negative reciprocal of the tangent slope. - Find both axis intercepts of the tangent line. - The axes and the line form a right triangle. - Use \(\frac{1}{2}(\text{base})(\text{height})\).

Solution

1. Differentiate: \(f'(x)=x\). 2. At \(x=2\), \(f(2)=0\) and the tangent slope is \(2\). Thus, the tangent line is \(y=2(x-2)=2x-4\). 3. The normal slope is the negative reciprocal, \(-\frac{1}{2}\). Thus, the normal line is \(y=-\frac{1}{2}(x-2)=-\frac{1}{2}x+1\). 4. The tangent line intersects the x-axis at \((2,0)\) and the y-axis at \((0,-4)\). 5. The right triangle has leg lengths \(2\) and \(4\), so its area is \(\frac{1}{2}\cdot 2\cdot 4=4\).

Answer

a) Tangent: \(y=2x-4\); normal: \(y=-\frac{1}{2}x+1\) b) \(4\) square units
52890212
Let \(f(x)=\frac{4}{x^2}\) for \(x\ne 0\). Find the equation of the tangent line at \(P=(a,f(a))\), where \(a\ne 0\), in terms of \(a\).

Hints

- Rewrite the rational expression using a negative exponent. - Find \(f'(a)\) and \(f(a)\). - Use point-slope form. - Apply exponent rules carefully when simplifying.

Solution

1. Rewrite the function as \(f(x)=4x^{-2}\). 2. Differentiate using the power rule: \(f'(x)=-8x^{-3}=-\frac{8}{x^3}\). 3. At \(x=a\), the tangent slope is \(-\frac{8}{a^3}\), and the point is \((a,\frac{4}{a^2})\). 4. Use point-slope form: \(y=-\frac{8}{a^3}(x-a)+\frac{4}{a^2}\). 5. Simplify: \(y=-\frac{8}{a^3}x+\frac{8}{a^2}+\frac{4}{a^2}=-\frac{8}{a^3}x+\frac{12}{a^2}\).

Answer

\(y=-\frac{8}{a^3}x+\frac{12}{a^2}\)
52891412
Let \(f(x)=\frac{2}{x}+x\). Find an equation of the tangent line to the graph at \(P=(1,f(1))\).

Hints

- Rewrite the reciprocal term using a negative exponent. - The derivative gives the tangent slope. - Use the point and slope to write the tangent line.

Solution

1. Find the point of tangency: \(f(1)=3\), so \(P=(1,3)\). 2. Rewrite \(f(x)=2x^{-1}+x\) and differentiate: \(f'(x)=-2x^{-2}+1=-\frac{2}{x^2}+1\). 3. Find the slope: \(f'(1)=-1\). 4. Use point-slope form: \(y-3=-(x-1)\), so \(y=-x+4\).

Answer

\(y=-x+4\)
52891612
For \(g(x)=x^2-3x\), tangent lines are drawn at \(x=1\) and \(x=2\). Find the angle at which the two tangent lines intersect.

Hints

- Find both tangent slopes using the derivative. - What slope relationship characterizes perpendicular lines? - You may also compare the lines' angles of inclination.

Solution

1. Differentiate: \(g'(x)=2x-3\). 2. The tangent slopes are \(g'(1)=-1\) and \(g'(2)=1\). 3. Since the product of the slopes is \((-1)(1)=-1\), the tangent lines are perpendicular. 4. Therefore, their angle of intersection is \(90^\circ\).

Answer

\(90^\circ\)
52891812
Find all values of \(a\) where the tangent line to \(f(x)=\frac{1}{3}x^3+x^2-6x\) is parallel to \(y=2x-5\).

Hints

- Parallel lines have equal slopes. - The derivative gives the tangent slope at \(a\). - Set the derivative equal to \(2\) and solve. - Check for more than one solution.

Solution

1. Differentiate: \(f'(x)=x^2+2x-6\). 2. The given line has slope \(2\), so require \(f'(a)=2\). 3. Solve \(a^2+2a-6=2\), or \(a^2+2a-8=0\). 4. Factor: \((a+4)(a-2)=0\). Thus, \(a=-4\) or \(a=2\).

Answer

\(a=-4\) and \(a=2\)
52898412
Find \(g'(x)\) for \(g(x)=\frac{2}{x^2}+6\sqrt{x}-x^3\), where \(x>0\). Write the answer without negative or fractional exponents.

Hints

- Rewrite reciprocals and radicals using negative or rational exponents. - Use \(\frac{1}{x^n}=x^{-n}\). - Use \(\sqrt{x}=x^{1/2}\). - Check the sign when differentiating a negative exponent.

Solution

1. Rewrite the function as \(g(x)=2x^{-2}+6x^{1/2}-x^3\). 2. Differentiate: \(g'(x)=-4x^{-3}+3x^{-1/2}-3x^2\). 3. Rewrite without negative or fractional exponents: \(g'(x)=-\frac{4}{x^3}+\frac{3}{\sqrt{x}}-3x^2\).

Answer

\(g'(x)=-\frac{4}{x^3}+\frac{3}{\sqrt{x}}-3x^2\), where \(x>0\)
52899812
At which points does the graph of \(f(x)=\frac{1}{3}x^3-\frac{1}{2}x^2-x\) have a tangent line that makes an angle of \(45^\circ\) with the positive x-axis? Give the coordinates of all such points.

Hints

- The derivative represents the tangent slope. - Convert the angle to a slope. - Solve the derivative equation for all possible inputs. - Substitute each input into the original function.

Solution

1. An angle of \(45^\circ\) corresponds to slope \(1\). 2. Differentiate: \(f'(x)=x^2-x-1\). 3. Set the derivative equal to \(1\): \(x^2-x-1=1\), so \(x^2-x-2=0\). 4. Factor: \((x-2)(x+1)=0\). Thus, \(x=2\) or \(x=-1\). 5. Evaluate the function: \(f(2)=-\frac{4}{3}\) and \(f(-1)=\frac{1}{6}\). The points are \((2,-\frac{4}{3})\) and \((-1,\frac{1}{6})\).

Answer

\((2,-\frac{4}{3})\) and \((-1,\frac{1}{6})\)
52900312
Let \(f(x)=x^2-2x+2\) and \(g(x)=-x^2+4x-2\). 1. Find the intersection points of the two graphs. 2. Find the acute angle at which the graphs intersect at each point.

Hints

- Set the function values equal to find intersection points. - Use each derivative to find the tangent slopes at an intersection. - Use the angle-between-lines formula for two known slopes. - Report the acute angle.

Solution

1. Set the functions equal: \(x^2-2x+2=-x^2+4x-2\). This simplifies to \(x^2-3x+2=0\), so \(x=1\) or \(x=2\). 2. The corresponding points are \((1,1)\) and \((2,2)\). 3. Differentiate: \(f'(x)=2x-2\) and \(g'(x)=-2x+4\). 4. At \(x=1\), the slopes are \(0\) and \(2\). Thus, \(\tan(\gamma)=\left|\frac{2-0}{1+0\cdot 2}\right|=2\), so \(\gamma=\arctan(2)\approx 63.43^\circ\). 5. At \(x=2\), the slopes are \(2\) and \(0\), giving the same value of \(\tan(\gamma)\). Therefore, the acute intersection angle is also approximately \(63.43^\circ\).

Answer

1. \((1,1)\) and \((2,2)\) 2. The acute intersection angle is approximately \(63.43^\circ\) at both points.
52900412
The graphs of \(f(x)=x^3-x\) and \(g(x)=x^2-1\) intersect at \(P=(-1,0)\) and \(Q=(1,0)\). Analyze the angle of intersection at each point.

Hints

- Find both derivative values at each intersection. - Equal tangent slopes give an intersection angle of \(0^\circ\). - Otherwise, use the angle-between-lines formula. - Use the acute angle between the tangent lines.

Solution

1. Differentiate: \(f'(x)=3x^2-1\) and \(g'(x)=2x\). 2. At \(P=(-1,0)\), the slopes are \(2\) and \(-2\). Therefore, \(\tan(\gamma)=\left|\frac{2-(-2)}{1+2(-2)}\right|=\frac{4}{3}\), so \(\gamma=\arctan(\frac{4}{3})\approx 53.13^\circ\). 3. At \(Q=(1,0)\), both slopes equal \(2\). The tangent lines coincide, so the intersection angle is \(0^\circ\); the graphs are tangent at \(Q\).

Answer

At \(P=(-1,0)\), the acute intersection angle is approximately \(53.13^\circ\). At \(Q=(1,0)\), the angle is \(0^\circ\); the graphs are tangent there.
52900512
Let \(f(x)=2x^2-4\). a) Find the equation of the normal line \(n\) at \(x=1\). b) Find the intercepts of this normal line with both coordinate axes. c) Describe the normal line at \(x=0\). Why can it not be written in the form \(y=mx+b\)?

Hints

- Tangent and normal slopes are negative reciprocals. - A line equation requires a point and a slope. - What does a tangent slope of \(0\) imply about the normal line? - Apply the vertical line test to a vertical line.

Solution

1. At \(x=1\), \(f(1)=-2\). Also, \(f'(x)=4x\), so the tangent slope is \(f'(1)=4\). 2. The normal slope is \(-\frac{1}{4}\). Through \((1,-2)\), the normal line is \(y+2=-\frac{1}{4}(x-1)\), or \(y=-\frac{1}{4}x-\frac{7}{4}\). 3. Setting \(x=0\) gives the y-intercept \(\left(0,-\frac{7}{4}\right)\). Setting \(y=0\) gives \(x=-7\), so the x-intercept is \((-7,0)\). 4. At \(x=0\), \(f'(0)=0\), so the tangent is horizontal. The normal is the vertical line through \((0,-4)\), namely \(x=0\). 5. A vertical line has undefined slope and assigns many y-values to the same x-value, so it cannot be written as a function \(y=mx+b\).

Answer

a) \(n: y=-0.25x-1.75\) b) The intercepts are \((0,-1.75)\) and \((-7,0)\). c) The normal is the y-axis, \(x=0\). It is vertical, so its slope is undefined and it is not a function of \(x\).
52900712
Let \(f(x)=\frac{1}{3}x^3-4x+10\) and \(g(x)=x^2-x-5\). Find all values of \(x\) where the tangent lines to the two graphs are parallel.

Hints

- Parallel lines have equal slopes. - Express each tangent slope using a derivative. - Set the derivative expressions equal. - Solve the resulting quadratic equation.

Solution

1. Differentiate: \(f'(x)=x^2-4\) and \(g'(x)=2x-1\). 2. Parallel tangent lines have equal slopes, so solve \(x^2-4=2x-1\). 3. Rearrange: \(x^2-2x-3=0\). 4. Factor: \((x-3)(x+1)=0\). Therefore, \(x=-1\) or \(x=3\).

Answer

\(x=-1\) and \(x=3\)
52900812
Let \(f(x)=x^3-3x^2+5\) and \(g(x)=3x^2-9x+2\). a) Find all values of \(x\) where the two graphs have the same slope. b) At the smaller of those values, find equations of the tangent lines to both graphs.

Hints

- Equal slopes mean equal derivative values. - Set the derivative functions equal and solve. - For each tangent line, use its own point on the corresponding graph. - Use point-slope form.

Solution

1. Differentiate: \(f'(x)=3x^2-6x\) and \(g'(x)=6x-9\). 2. Set the slopes equal: \(3x^2-6x=6x-9\). Dividing by \(3\) gives \(x^2-4x+3=0\), so \(x=1\) or \(x=3\). 3. The smaller value is \(x=1\). The common slope is \(-3\). 4. Since \(f(1)=3\), the tangent to \(f\) is \(y-3=-3(x-1)\), or \(y=-3x+6\). 5. Since \(g(1)=-4\), the tangent to \(g\) is \(y+4=-3(x-1)\), or \(y=-3x-1\).

Answer

a) \(x=1\) and \(x=3\) b) At \(x=1\), the tangent lines are \(y=-3x+6\) and \(y=-3x-1\).
52901112
Let \(f(x)=x^2\) and \(g(x)=(x-2)^2\). a) Find the intersection point \(P\) of the two graphs. b) At \(P\), tangent lines are drawn to both graphs. Find the x-intercept of each tangent line. c) The two tangent lines and the x-axis form a triangle. Find its area.

Hints

- Set the two function values equal to find their common point. - Use each derivative to find the tangent slopes at that point. - Set \(y=0\) to find each tangent line's x-intercept. - Use the x-axis segment as the base of the triangle.

Solution

1. Set the functions equal: \(x^2=(x-2)^2\). This simplifies to \(x=1\), and the common value is \(1\). Thus, \(P=(1,1)\). 2. Differentiate: \(f'(x)=2x\) and \(g'(x)=2(x-2)\). At \(x=1\), the slopes are \(2\) and \(-2\). 3. The tangent lines are \(y-1=2(x-1)\), or \(y=2x-1\), and \(y-1=-2(x-1)\), or \(y=-2x+3\). 4. Setting \(y=0\) gives x-intercepts \(x=\frac{1}{2}\) and \(x=\frac{3}{2}\). 5. The base on the x-axis has length \(1\), and the height from \(P\) is \(1\). Therefore, the area is \(\frac{1}{2}\).

Answer

a) \(P=(1,1)\) b) The tangent lines meet the x-axis at \((\frac{1}{2},0)\) and \((\frac{3}{2},0)\). c) \(\frac{1}{2}\) square unit
52901212
Consider \(f(x)=\sqrt{x}\) and \(g(x)=\frac{1}{x}\) for \(x>0\). a) Find equations of the tangent lines to both graphs at their common point \(P=(1,1)\). b) The two tangent lines and the y-axis form a triangle. Find its area.

Hints

- Differentiate the square-root and reciprocal functions using power notation. - Use point-slope form at \((1,1)\). - The triangle's base lies on the y-axis. - The x-coordinate of \(P\) gives the height relative to that base.

Solution

1. Differentiate: \(f'(x)=\frac{1}{2\sqrt{x}}\) and \(g'(x)=-\frac{1}{x^2}\). 2. At \(x=1\), the slopes are \(\frac{1}{2}\) and \(-1\). 3. The tangent to \(f\) is \(y-1=\frac{1}{2}(x-1)\), or \(y=\frac{1}{2}x+\frac{1}{2}\). 4. The tangent to \(g\) is \(y-1=-(x-1)\), or \(y=-x+2\). 5. Their y-intercepts are \(\frac{1}{2}\) and \(2\), so the vertical base has length \(\frac{3}{2}\). The horizontal distance from \(P\) to the y-axis is \(1\). 6. The area is \(\frac{1}{2}\cdot\frac{3}{2}\cdot 1=\frac{3}{4}\).

Answer

a) \(y=\frac{1}{2}x+\frac{1}{2}\) and \(y=-x+2\) b) \(\frac{3}{4}\) square unit
52901912
A tangent line to \(f(x)=\frac{1}{2}x^2\) is drawn at \(x=x_1\), and a tangent line to \(g(x)=\frac{1}{x}\) is drawn at \(x=x_2\). Find the relationship between \(x_1\) and \(x_2\) that makes the tangent lines perpendicular.

Hints

- Use each derivative to express a tangent slope. - What relationship do the slopes of perpendicular lines satisfy? - Write one equation involving \(x_1\) and \(x_2\). - Solve for one input in terms of the other.

Solution

1. Differentiate: \(f'(x)=x\) and \(g'(x)=-\frac{1}{x^2}\). 2. Perpendicular nonvertical lines have slopes whose product is \(-1\). Thus, \(f'(x_1)g'(x_2)=-1\). 3. Substitute: \(x_1(-\frac{1}{x_2^2})=-1\). 4. Since \(x_2\ne 0\), this simplifies to \(x_1=x_2^2\).

Answer

\(x_1=x_2^2\), with \(x_2\ne 0\)
52902112
Let \(f(x)=x^2+3x\) and \(g(x)=-x^2+5\). a) Find the intersection points of the two graphs. b) At what value of \(x\) do the tangent lines to the two graphs have the same slope? c) Find an equation of the normal line to the graph of \(g\) at \(x=2\).

Hints

- Set the function values equal to find intersections. - Equal tangent slopes mean equal derivative values. - The normal slope is the negative reciprocal of the tangent slope. - Use point-slope form for the normal line.

Solution

1. Set the functions equal: \(x^2+3x=-x^2+5\), so \(2x^2+3x-5=0\). The solutions are \(x=1\) and \(x=-\frac{5}{2}\). 2. The intersection points are \((1,4)\) and \((-\frac{5}{2},-\frac{5}{4})\). 3. Differentiate: \(f'(x)=2x+3\) and \(g'(x)=-2x\). Equal slopes require \(2x+3=-2x\), so \(x=-\frac{3}{4}\). 4. At \(x=2\), \(g(2)=1\) and the tangent slope is \(-4\). The normal slope is \(\frac{1}{4}\). 5. The normal line is \(y-1=\frac{1}{4}(x-2)\), or \(y=\frac{1}{4}x+\frac{1}{2}\).

Answer

a) \((1,4)\) and \((-\frac{5}{2},-\frac{5}{4})\) b) \(x=-\frac{3}{4}\) c) \(y=\frac{1}{4}x+\frac{1}{2}\)
52902212
Let \(h(x)=\frac{1}{4}x^2-x\). a) Find the point \(P\) where the tangent line is parallel to the x-axis. b) Find the general equation of the tangent line \(t_a\) at an arbitrary input \(a\). c) Show that the y-intercept of \(t_a\) is always \(S=(0,-\frac{1}{4}a^2)\).

Hints

- A tangent parallel to the x-axis has slope \(0\). - Write the tangent line at \(x=a\) using point-slope form. - Treat \(a\) as a fixed parameter while simplifying. - Set \(x=0\) to find the y-intercept.

Solution

1. Differentiate: \(h'(x)=\frac{1}{2}x-1\). A horizontal tangent has slope \(0\), so \(\frac{1}{2}x-1=0\), giving \(x=2\). 2. Since \(h(2)=-1\), the point is \(P=(2,-1)\). 3. At \(x=a\), the slope is \(\frac{1}{2}a-1\), and the point is \((a,\frac{1}{4}a^2-a)\). 4. Point-slope form gives \(y=(\frac{1}{2}a-1)(x-a)+\frac{1}{4}a^2-a\). 5. Simplifying gives \(t_a: y=(\frac{1}{2}a-1)x-\frac{1}{4}a^2\). 6. Setting \(x=0\) gives \(y=-\frac{1}{4}a^2\), so the y-intercept is \((0,-\frac{1}{4}a^2)\).

Answer

a) \(P=(2,-1)\) b) \(t_a: y=(\frac{1}{2}a-1)x-\frac{1}{4}a^2\) c) Setting \(x=0\) gives \(S=(0,-\frac{1}{4}a^2)\).
52904112
Find all points on the graph of \(f(x)=x^3-3x^2-6x+2\) where the tangent line has slope \(3\). Find the equation of the tangent line at each point.

Hints

- Set the derivative equal to the required slope. - Solve for every possible input. - Substitute each input into the original function. - Use the common slope and each point to write the tangent lines.

Solution

1. Differentiate: \(f'(x)=3x^2-6x-6\). 2. Set the derivative equal to \(3\): \(3x^2-6x-6=3\). Dividing by \(3\) gives \(x^2-2x-3=0\). 3. Factor: \((x-3)(x+1)=0\), so \(x=3\) or \(x=-1\). 4. Evaluate the function: \(f(3)=-16\) and \(f(-1)=4\). The points are \((3,-16)\) and \((-1,4)\). 5. At \((3,-16)\), the tangent is \(y+16=3(x-3)\), or \(y=3x-25\). 6. At \((-1,4)\), the tangent is \(y-4=3(x+1)\), or \(y=3x+7\).

Answer

The points are \((3,-16)\) and \((-1,4)\). The tangent lines are \(y=3x-25\) and \(y=3x+7\), respectively.
52905212
Consider the functions \(f(x)=0.5x^2-2\), \(g(x)=-0.125x^2+0.5\), and \(h(x)=\frac{2}{x}-1\). 1. Find the positive zero \(x_0\) of \(f\). 2. Determine whether the graphs of \(g\) and \(h\) also cross the x-axis at \(x_0\). 3. Determine whether the graphs of \(g\) and \(h\) intersect the graph of \(f\) at right angles at \(x_0\).

Hints

- What must a function value equal where its graph crosses the x-axis? - Recall the power rule, including its use with negative exponents. - What relationship between two nonzero slopes indicates perpendicular tangent lines? - Compare the products of the derivatives at the common point.

Solution

1. Solve \(0.5x^2-2=0\): \(x^2=4\), so \(x=\pm2\). The positive zero is \(x_0=2\). 2. Evaluate the other functions at \(x=2\): \(g(2)=-0.125\cdot2^2+0.5=0\) and \(h(2)=\frac{2}{2}-1=0\). Therefore, all three graphs pass through \((2,0)\). 3. Differentiate: \(f'(x)=x\), \(g'(x)=-0.25x\), and \(h'(x)=-\frac{2}{x^2}\). At \(x=2\), the slopes are \(f'(2)=2\) and \(g'(2)=h'(2)=-0.5\). Since \(2\cdot(-0.5)=-1\), each of the other two graphs intersects the graph of \(f\) at a right angle.

Answer

1. \(x_0=2\) 2. Yes. All three graphs cross the x-axis at \((2,0)\). 3. Yes. The products of the tangent slopes are \(f'(2)g'(2)=-1\) and \(f'(2)h'(2)=-1\).
52933012
Consider the family of functions \(g_k(x)=k(x-2)^3+x^2+1\), where \(k\in\mathbb{R}\). Show that there is a point at which every graph in the family has the same tangent line. Find the equation of that tangent line.

Hints

- A common tangent requires both a common point and a common derivative value. - Look for an input that makes the term containing \(k\) equal to zero. - Use the point and slope to write the tangent line.

Solution

1. For the function value to be independent of \(k\), the parameter term must be zero. Since \((x-2)^3=0\), use \(x=2\). 2. Evaluate the function: \(g_k(2)=k(2-2)^3+2^2+1=5\). Every graph passes through \((2,5)\). 3. Differentiate: \(g_k'(x)=3k(x-2)^2+2x\). 4. Evaluate the derivative at \(x=2\): \(g_k'(2)=4\), independent of \(k\). 5. The line with slope \(4\) through \((2,5)\) is \(y-5=4(x-2)\), or \(y=4x-3\).

Answer

Every graph has the same tangent line at \((2,5)\). Its equation is \(y=4x-3\).
53000812
Find a quadratic polynomial \(p\) whose graph is tangent to \(f(x)=\ln(x+1)\) at the origin and passes through \(A(2, 4)\).

Hints

- Tangent graphs have the same function value and derivative at the point of tangency. - Start with the general form of a quadratic polynomial. - Use the point \(A\) to determine the remaining coefficient. - Check that the leading coefficient is nonzero.

Solution

1. Write \(p(x)=ax^2+bx+c\). 2. Since the graphs are tangent at the origin, they have the same value and slope there. Because \(f(0)=0\), \(p(0)=0\), so \(c=0\). 3. Since \(f'(x)=\frac{1}{x+1}\), \(f'(0)=1\). Also, \(p'(x)=2ax+b\), so \(p'(0)=b=1\). 4. Thus \(p(x)=ax^2+x\). Using \(p(2)=4\), \(4a+2=4\), so \(a=\frac{1}{2}\). 5. Therefore, \(p(x)=\frac{1}{2}x^2+x\).

Answer

\(p(x)=\frac{1}{2}x^2+x\)
53001012
A cubic polynomial \(p\) is tangent to \(f(x)=4e^{-0.5x}\) at \(x=0\). Its graph also has a horizontal tangent at \(x=-1\) and passes through \(Q(1, 2)\). Find \(p(x)\).

Hints

- Start with the general form of a cubic polynomial. - Tangency at \(x=0\) gives one condition for the value and one for the slope. - A horizontal tangent means the derivative is zero. - Use all conditions to form and solve a linear system.

Solution

1. Write \(p(x)=ax^3+bx^2+cx+d\), so \(p'(x)=3ax^2+2bx+c\). 2. Tangency at \(x=0\) requires equal function values and slopes. Since \(f(0)=4\), \(d=4\). 3. Differentiate \(f\): \(f'(x)=-2e^{-0.5x}\), so \(f'(0)=-2\). Therefore, \(c=-2\). 4. The horizontal tangent at \(x=-1\) gives \(p'(-1)=3a-2b-2=0\), so \(3a-2b=2\). 5. Since \(p(1)=2\), \(a+b-2+4=2\), so \(a+b=0\). 6. Solving the system gives \(a=\frac{2}{5}\) and \(b=-\frac{2}{5}\). 7. Therefore, \(p(x)=\frac{2}{5}x^3-\frac{2}{5}x^2-2x+4\).

Answer

\(p(x)=\frac{2}{5}x^3-\frac{2}{5}x^2-2x+4\)
53021912
Let \(f(x)=\frac{1}{2}x^3-2x^2+x\). a) Find the tangent line from the origin to the graph of \(f\) whose point of tangency \(B\) is not the origin. Give the coordinates of \(B\). b) Show that this tangent line is perpendicular to the tangent line to the graph at the origin.

Hints

- A tangent line through the origin has equation \(y=mx\). - At the point of tangency, use \(m=f'(x_0)\) and \(f(x_0)=mx_0\). - Perpendicular nonvertical lines have slopes whose product is \(-1\).

Solution

1. Differentiate: \(f'(x)=\frac{3}{2}x^2-4x+1\). 2. A tangent line through the origin at \(x=x_0\) must satisfy \(f(x_0)=f'(x_0)x_0\). 3. Substitute: \(\frac{1}{2}x_0^3-2x_0^2+x_0=x_0\left(\frac{3}{2}x_0^2-4x_0+1\right)\). 4. Simplifying gives \(x_0^2(x_0-2)=0\). The solutions are \(x_0=0\) and \(x_0=2\). Since the point of tangency is not the origin, \(x_0=2\). 5. Since \(f(2)=-2\), the point of tangency is \(B(2, -2)\). The tangent slope is \(f'(2)=-1\), so the tangent line is \(t: y=-x\). 6. At the origin, the tangent slope is \(f'(0)=1\). Because \((-1)(1)=-1\), the two tangent lines are perpendicular.

Answer

a) \(B(2, -2)\); \(t: y=-x\) b) The slopes are \(-1\) and \(1\), whose product is \(-1\), so the tangent lines are perpendicular.
53242512
The graphs of \(f(x)=x^2-6x+9\) and \(g(x)=-x+5\) intersect at two points, \(P_1\) and \(P_2\), as shown. Let \(P_1\) be the point with the smaller x-coordinate. The angle of intersection of two graphs is the acute angle formed by their tangent lines at the intersection point. a) Find the coordinates of \(P_1\) and \(P_2\). b) Find the slopes of the tangent lines to the graphs of \(f\) and \(g\) at each intersection point. c) Find the angles of intersection \(\alpha_1\) at \(P_1\) and \(\alpha_2\) at \(P_2\). Give each answer in degrees to the nearest hundredth.
Figure for problem 532425

Hints

- Set the two function expressions equal to find their intersection points. - The derivative gives the tangent slope at an input. - Relate the slope of a line to its angle of inclination. - Use the acute-angle formula for two lines, and make sure the result is at most \(90^\circ\).

Solution

1. Set the functions equal: \(x^2-6x+9=-x+5\). Then \(x^2-5x+4=0\), so \((x-1)(x-4)=0\). Thus, \(x=1\) or \(x=4\). 2. Using \(g(x)=-x+5\), the intersection points are \(P_1(1,4)\) and \(P_2(4,1)\). 3. Differentiate: \(f'(x)=2x-6\) and \(g'(x)=-1\). At \(P_1\), the slopes are \(f'(1)=-4\) and \(g'(1)=-1\). At \(P_2\), the slopes are \(f'(4)=2\) and \(g'(4)=-1\). 4. For two lines with slopes \(m_1\) and \(m_2\), \(\tan(\alpha)=\left|\frac{m_1-m_2}{1+m_1m_2}\right|\). At \(P_1\), \(\tan(\alpha_1)=\left|\frac{-4-(-1)}{1+(-4)(-1)}\right|=0.6\), so \(\alpha_1\approx30.96^\circ\). 5. At \(P_2\), \(\tan(\alpha_2)=\left|\frac{2-(-1)}{1+2(-1)}\right|=3\), so \(\alpha_2\approx71.57^\circ\).

Answer

a) \(P_1(1,4)\) and \(P_2(4,1)\) b) At \(P_1\), the slopes are \(-4\) for \(f\) and \(-1\) for \(g\). At \(P_2\), the slopes are \(2\) for \(f\) and \(-1\) for \(g\). c) \(\alpha_1\approx30.96^\circ\) and \(\alpha_2\approx71.57^\circ\)
53242812
Let \(f(x)=-0.25x^2+x+3\). The point \(Q(0,7)\) is shown above the graph of \(f\). Two tangent lines to the graph of \(f\) pass through \(Q\). a) Find the coordinates of the two points of tangency, \(B_1\) and \(B_2\). b) Find equations of the two tangent lines, \(t_1\) and \(t_2\).
Figure for problem 532428

Hints

- Write the tangent-line equation at a general input. - A line through \(Q(0,7)\) must have a y-value of \(7\) when \(x=0\). - Express the tangent slope using the derivative and also using the point of tangency and \(Q\). - Equate the two slope expressions to solve for the possible inputs.

Solution

1. The tangent line at \(x=u\) is \(t(x)=f'(u)(x-u)+f(u)\). 2. Differentiate: \(f'(x)=-0.5x+1\). Therefore, \(t(x)=(-0.5u+1)(x-u)+(-0.25u^2+u+3)\). 3. Since the tangent passes through \(Q(0,7)\), set \(t(0)=7\): \((-0.5u+1)(-u)-0.25u^2+u+3=7\). This simplifies to \(0.25u^2=4\), so \(u=4\) or \(u=-4\). 4. Evaluate the function: \(f(4)=3\) and \(f(-4)=-5\). The points of tangency are \(B_1(4,3)\) and \(B_2(-4,-5)\). 5. The slopes are \(f'(4)=-1\) and \(f'(-4)=3\). Thus, \(t_1\) is \(y-3=-(x-4)\), or \(y=-x+7\), and \(t_2\) is \(y+5=3(x+4)\), or \(y=3x+7\).

Answer

a) \(B_1(4,3)\) and \(B_2(-4,-5)\) b) \(t_1: y=-x+7\) and \(t_2: y=3x+7\)
53252812
Let \(f(x)=\frac{1}{6}x^3-x^2+2\). Its graph is shown. a) Find \(f'(x)\). b) Find the point \(A(a,f(a))\) where the graph of \(f\) has slope \(-2\). c) Find the points where the tangent line to the graph of \(f\) is parallel to the line \(y=6x-1\).
Figure for problem 532528

Hints

- The slope of the graph at an input is the derivative value there. - Apply the power rule to find the derivative. - For part b), set the derivative equal to the given slope. - Parallel lines have equal slopes. - After finding each x-coordinate, evaluate the original function to obtain the full point.

Solution

1. Differentiate: \(f'(x)=\frac{1}{2}x^2-2x\). 2. Set the derivative equal to \(-2\): \(\frac{1}{2}a^2-2a=-2\). This gives \(a^2-4a+4=0\), so \(a=2\). 3. Evaluate the function: \(f(2)=\frac{1}{6}\cdot2^3-2^2+2=-\frac{2}{3}\). Thus, \(A\left(2,-\frac{2}{3}\right)\). 4. A line parallel to \(y=6x-1\) has slope \(6\). Set \(\frac{1}{2}x^2-2x=6\). Then \(x^2-4x-12=0\), so \((x-6)(x+2)=0\). Therefore, \(x=6\) or \(x=-2\). 5. Evaluate the function: \(f(6)=2\) and \(f(-2)=-\frac{10}{3}\). The points are \((6,2)\) and \(\left(-2,-\frac{10}{3}\right)\).

Answer

a) \(f'(x)=\frac{1}{2}x^2-2x\) b) \(A\left(2,-\frac{2}{3}\right)\) c) \((6,2)\) and \(\left(-2,-\frac{10}{3}\right)\)
53261812
The graph of a quadratic function \(f(x)=ax^2+bx\) is shown. a) Use suitable points from the graph to find \(a\) and \(b\). b) Find the equation of the normal line \(n\) at \(P(3,f(3))\). c) The normal line and the coordinate axes form a right triangle. Find its area.
Figure for problem 532618

Hints

- Read two exact points from the graph and substitute them into \(f(x)=ax^2+bx\). - Evaluate \(f(3)\) and use the derivative for the tangent slope. - Convert the tangent slope to the normal slope. - Use the normal line's axis intercepts as the triangle's legs.

Solution

1. From the graph, use \((2,2)\) and \((4,0)\). Substitution gives \(4a+2b=2\) and \(16a+4b=0\). 2. Simplifying gives \(2a+b=1\) and \(4a+b=0\). Subtracting yields \(a=-0.5\), and then \(b=2\). Thus, \(f(x)=-0.5x^2+2x\). 3. Evaluate the function: \(f(3)=1.5\), so \(P=(3,1.5)\). Differentiate: \(f'(x)=-x+2\), so the tangent slope at \(x=3\) is \(-1\). 4. The normal slope is \(1\). Through \(P\), the normal is \(y-1.5=x-3\), or \(y=x-1.5\). 5. Its intercepts are \((0,-1.5)\) and \((1.5,0)\). The triangle area is \(\frac{1}{2}(1.5)(1.5)=1.125=\frac{9}{8}\) square units.

Answer

a) \(a=-0.5\), \(b=2\) b) \(n: y=x-1.5\) c) \(\frac{9}{8}\) square units
53266112
The functions \(f\) and \(g\) are defined by \(f(x) = 0.5x^2 - 2\) and \(g(x) = -0.2x^3 + 1.5x\). The four figures show the graphs of \(f\), \(g\), \(f'\), and \(g'\) in a random order. Match each graph, (1) through (4), with the correct function. Justify your matches.
Figure for problem 532661

Hints

- First compute \(f'(x)\) and \(g'(x)\). - Compare each graph's degree, symmetry, vertex, and intercepts. - Check that the zeros of each derivative match horizontal tangents of its function.

Solution

1. Differentiate: \(f'(x) = x\) and \(g'(x) = -0.6x^2 + 1.5\). 2. Graph (3) is an upward-opening parabola with vertex \((0, -2)\), so it represents \(f\). Graph (1) is the line \(y = x\), so it represents \(f'\). 3. Graph (2) is an odd cubic with negative leading coefficient, so it represents \(g\). Graph (4) is a downward-opening parabola with vertex \((0, 1.5)\), so it represents \(g'\).

Answer

(1) \(f'\) (2) \(g\) (3) \(f\) (4) \(g'\)
53277812
The graph of \(f(x)=-0.25x^2+4\) is shown. a) Find the x-intercepts \(P\) and \(Q\) of the graph. b) Find equations of the tangent lines \(t_1\) and \(t_2\) at \(P\) and \(Q\), respectively. c) The tangent lines intersect at \(S\). Find the area of triangle \(PQS\).
Figure for problem 532778

Hints

- Set the function equal to zero to find the x-intercepts. - Use the derivative to find each tangent slope. - Use a point and its slope to write each tangent line. - Solve the two tangent equations as a system to find \(S\). - Use the triangle area formula with \(\overline{PQ}\) as the base.

Solution

1. Set \(f(x)=0\): \(-0.25x^2+4=0\), so \(x^2=16\) and \(x=\pm4\). Thus, \(P=(-4,0)\) and \(Q=(4,0)\). 2. Differentiate: \(f'(x)=-0.5x\). At \(P\), the slope is \(f'(-4)=2\), so \(t_1\) is \(y=2(x+4)=2x+8\). 3. At \(Q\), the slope is \(f'(4)=-2\), so \(t_2\) is \(y=-2(x-4)=-2x+8\). 4. Set the tangent equations equal: \(2x+8=-2x+8\), giving \(x=0\) and \(y=8\). Thus, \(S=(0,8)\). 5. Triangle \(PQS\) has base \(8\) and height \(8\). Its area is \(\frac{1}{2}\cdot8\cdot8=32\) square units.

Answer

a) \(P=(-4,0)\) and \(Q=(4,0)\) b) \(t_1: y=2x+8\) and \(t_2: y=-2x+8\) c) \(32\) square units
53380612
The figures show the graphs of \(f(x) = x^2 - 2x\), its derivative \(f'\), \(g(x) = f(x) + 3\), and \(h(x) = f(x + 2)\). Match each function description with graphs I through IV.
Figure for problem 533806

Hints

- Identify the vertex and zeros of \(f\). - Adding outside the function shifts a graph vertically; adding inside the input shifts it horizontally. - The derivative of a quadratic function is linear.

Solution

1. The graph of \(f(x) = x^2 - 2x\) is an upward-opening parabola with zeros at \(x = 0\) and \(x = 2\) and vertex \((1, -1)\). This is graph II. 2. The derivative is \(f'(x) = 2x - 2\), a line with slope \(2\) and \(y\)-intercept \(-2\). This is graph IV. 3. The graph of \(g(x) = f(x) + 3\) is shifted up \(3\) units, so its vertex is \((1, 2)\). This is graph I. 4. The graph of \(h(x) = f(x + 2)\) is shifted left \(2\) units, so its vertex is \((-1, -1)\). This is graph III.

Answer

Graph I: \(g(x) = f(x) + 3\) Graph II: \(f(x)\) Graph III: \(h(x) = f(x + 2)\) Graph IV: \(f'(x)\)
53392312
Let \(f(x)=x^2-1\) and \(g(x)=7-x^2\). Their graphs intersect at two points. a) Find the coordinates of both intersection points. b) Find the acute angle at which the graphs intersect at each point.
Figure for problem 533923

Hints

- Set the function expressions equal to find the intersections. - The angle between the curves is the angle between their tangent lines. - Use derivatives to find the tangent slopes. - Apply the formula for the acute angle between two lines.

Solution

1. Set the functions equal: \(x^2-1=7-x^2\). Then \(2x^2=8\), so \(x=\pm2\). 2. Since \(f(2)=f(-2)=3\), the intersection points are \((2,3)\) and \((-2,3)\). 3. Differentiate: \(f'(x)=2x\) and \(g'(x)=-2x\). At \(x=2\), the tangent slopes are \(4\) and \(-4\). 4. Use \(\tan(\phi)=\left|\frac{m_1-m_2}{1+m_1m_2}\right|\): \(\tan(\phi)=\left|\frac{4-(-4)}{1+4(-4)}\right|=\frac{8}{15}\). Thus, \(\phi=\arctan\left(\frac{8}{15}\right)\approx28.1^\circ\). 5. By symmetry, the acute angle at the other intersection point is also approximately \(28.1^\circ\).

Answer

a) \((2,3)\) and \((-2,3)\) b) The angle at each intersection is approximately \(28.1^\circ\).
53393312
Consider the parabola \(f(x)=x^2\). At the point \(P(u,u^2)\), where \(u>0\), let \(t\) be the tangent line to the graph. The diagram illustrates the case \(u=2\). a) Show algebraically that \(t\) always intersects the y-axis at \(Q(0,-u^2)\). b) Let \(P_1\) be the horizontal projection of \(P\) onto the y-axis. Compare the distance from \(Q\) to the origin with the distance from \(P_1\) to the origin. What do you observe?
Figure for problem 533933

Hints

- Use the derivative at \(x=u\) to find the tangent slope. - Write the tangent equation in point-slope form. - Set \(x=0\) to find the y-intercept. - The projection \(P_1\) has x-coordinate \(0\) and the same y-coordinate as \(P\).

Solution

1. Differentiate: \(f'(x)=2x\). 2. At \(x=u\), the tangent line is \(y=2u(x-u)+u^2=2ux-u^2\). 3. At the y-axis, \(x=0\), so \(y=-u^2\). Therefore, the y-intercept is \(Q(0,-u^2)\). 4. The projection point is \(P_1(0,u^2)\). 5. The distance from \(Q\) to the origin is \(|-u^2|=u^2\), and the distance from \(P_1\) to the origin is \(|u^2|=u^2\). 6. The distances are equal, so the origin is the midpoint of \(\overline{P_1Q}\).

Answer

a) \(t: y=2ux-u^2\), so its y-intercept is \(Q(0,-u^2)\). b) Both distances equal \(u^2\). The origin is the midpoint of \(\overline{P_1Q}\).
53423212
Consider the functions \(f(x) = \frac{1}{3}x^3 - x\) and \(g(x) = \frac{1}{4}x^4 - 2x^2\). Which graph, A, B, C, or D, represents \(f'\), and which represents \(g'\)? Justify your choices by comparing zeros, symmetry, or other key features.
Figure for problem 534232

Hints

- Differentiate \(f\) and \(g\) first. - Compare the degree and symmetry of each derivative with the graphs. - Find the zeros of each derivative and match them to the \(x\)-intercepts shown.

Solution

1. Differentiate each function using the power rule: \(f'(x) = x^2 - 1\) and \(g'(x) = x^3 - 4x\). 2. The graph of \(f'\) is an upward-opening parabola, symmetric about the \(y\)-axis, with vertex \((0, -1)\) and zeros at \(x=-1\) and \(x=1\). This is graph A. 3. Since \(g'(x)=x(x-2)(x+2)\), its graph is an odd cubic with zeros at \(x=-2\), \(x=0\), and \(x=2\). This is graph B.

Answer

Graph A represents \(f'\), and graph B represents \(g'\).
53424212
Let \(f(x)=\frac{1}{2}x^2+2\). For each \(a\in\mathbb{R}\), let \(Q_a(a,f(a))\) be the corresponding point on the graph. Let \(P=(0,0)\). a) For \(a\ne0\), find the slope \(m_a\) of the secant line through \(P\) and \(Q_a\) in terms of \(a\). b) Let \(t_a\) be the tangent line to \(f\) at \(Q_a\). Find every value of \(a\) for which \(t_a\) passes through \(P\).
Figure for problem 534242

Hints

- Use the slope formula for the two known points. - Write the tangent equation at a general input \(a\). - A point lies on a line when its coordinates satisfy the line equation. - Use the derivative to express the tangent slope.

Solution

1. The point is \(Q_a\left(a,\frac{1}{2}a^2+2\right)\). 2. The secant slope is \(m_a=\frac{f(a)-0}{a-0}=\frac{\frac{1}{2}a^2+2}{a}=\frac{a^2+4}{2a}\). 3. Differentiate: \(f'(x)=x\). 4. The tangent at \(Q_a\) is \(y=a(x-a)+\frac{1}{2}a^2+2=ax-\frac{1}{2}a^2+2\). 5. For this line to pass through \(P=(0,0)\), \(0=-\frac{1}{2}a^2+2\). Thus, \(a^2=4\), so \(a=2\) or \(a=-2\).

Answer

a) \(m_a=\frac{a^2+4}{2a}\) b) \(a=2\) and \(a=-2\)
53424312
Let \(g(x)=\frac{2}{x}\) for \(x>0\). For \(a>0\), let \(Q_a(a, g(a))\) be a point on the graph. The point \(P(0, 4)\) lies on the y-axis. a) Find the equation of the tangent line \(t_a\) at \(Q_a\) in terms of \(a\). b) Find the value of \(a>0\) for which \(t_a\) passes through \(P\).
Figure for problem 534243

Hints

- Rewrite the function using a negative exponent before differentiating. - Use point-slope form at \(x=a\). - A point on the y-axis has x-coordinate \(0\). - Substitute the coordinates of \(P\) into the tangent-line equation.

Solution

1. Differentiate: \(g'(x)=-\frac{2}{x^2}\). 2. The tangent line at \(x=a\) is \(y=g'(a)(x-a)+g(a)=-\frac{2}{a^2}(x-a)+\frac{2}{a}\). 3. Simplify: \(t_a: y=-\frac{2}{a^2}x+\frac{4}{a}\). 4. Since the line passes through \(P(0, 4)\), \(4=\frac{4}{a}\). Therefore, \(a=1\).

Answer

a) \(t_a: y=-\frac{2}{a^2}x+\frac{4}{a}\) b) \(a=1\)
53486012
The coordinate plane shows the graph of a quadratic function \(f\). The graph crosses the x-axis at the origin and at \(x=4\). The tangent lines at these two intercepts meet at \(S(2, -6)\). Find \(f(x)\).
Figure for problem 534860

Hints

- Use the factored form of a quadratic with the given zeros. - Differentiate to find the tangent slope at the origin. - Write the tangent line through the origin. - Substitute the tangent lines' intersection point to determine the remaining coefficient.

Solution

1. Since the zeros are \(0\) and \(4\), write \(f(x)=ax(x-4)=ax^2-4ax\). 2. Differentiate: \(f'(x)=2ax-4a\). At the origin, the tangent slope is \(f'(0)=-4a\), so the tangent line there is \(y=-4ax\). 3. The point \(S(2, -6)\) lies on this tangent line. Therefore, \(-6=-4a(2)=-8a\), so \(a=\frac{3}{4}\). 4. Thus \(f(x)=\frac{3}{4}x(x-4)=\frac{3}{4}x^2-3x\).

Answer

\(f(x)=\frac{3}{4}x^2-3x\)
52232512
A light ray starts at the origin \(O=(0,0)\) and is tangent to the parabolic boundary \(f(x)=\frac{1}{8}x^2+2\) in the region \(x>0\). Find the point of tangency \(B\) and the slope of the light ray.

Hints

- Write a general tangent line at an unknown input \(u\). - The tangent slope at \(u\) is \(f'(u)\). - Require the tangent line to pass through the given external point. - Use the condition \(x>0\) when choosing a solution.

Solution

1. Differentiate: \(f'(x)=\frac{1}{4}x\). 2. Let the point of tangency have x-coordinate \(u\). The tangent line is \(y=f'(u)(x-u)+f(u)\). 3. Substitute the expressions for \(f'(u)\) and \(f(u)\): \(y=\frac{1}{4}u(x-u)+\frac{1}{8}u^2+2=\frac{1}{4}ux-\frac{1}{8}u^2+2\). 4. The tangent passes through \((0,0)\), so \(0=-\frac{1}{8}u^2+2\). Thus, \(u^2=16\). Because \(u>0\), \(u=4\). 5. Find the point and slope: \(f(4)=4\) and \(f'(4)=1\). Therefore, \(B=(4,4)\) and the ray has slope \(1\).

Answer

\(B=(4,4)\) and \(m=1\)
52232612
Let \(h(x)=x^2-4x+5\). Tangent lines are drawn from the point \(P=(2,0)\), which is not on the graph of \(h\). Find the points of tangency and the equations of both tangent lines.

Hints

- A tangent at input \(u\) has slope \(h'(u)\). - Write the tangent line at the unknown point of tangency. - Require that line to pass through \(P=(2,0)\). - The resulting equation may have more than one solution for \(u\).

Solution

1. Differentiate: \(h'(x)=2x-4\). 2. Let the point of tangency be \(B=(u,h(u))\). A tangent line at \(u\) is \(y=(2u-4)(x-u)+u^2-4u+5\). 3. Require the line to pass through \(P=(2,0)\): \(0=(2u-4)(2-u)+u^2-4u+5\). 4. Simplifying gives \(u^2-4u+3=0\), so \(u=1\) or \(u=3\). 5. The points of tangency are \((1,h(1))=(1,2)\) and \((3,h(3))=(3,2)\). 6. At \(u=1\), the slope is \(-2\), giving \(y=-2(x-2)=-2x+4\). At \(u=3\), the slope is \(2\), giving \(y=2(x-2)=2x-4\).

Answer

The points of tangency are \((1,2)\) and \((3,2)\). The tangent lines are \(y=-2x+4\) and \(y=2x-4\), respectively.
52232912
For each \(k>0\), let \(f_k(x)=x^2-kx\). The graph intersects the x-axis at the origin \(O=(0,0)\) and at another point \(A\). Tangent lines at \(O\) and \(A\) intersect at \(S\). Find \(k\) so that triangle \(OAS\) has area \(16\) square units.

Hints

- First find the two x-intercepts of the parabola. - Use the derivative to write both tangent lines. - Their intersection is the third vertex of the triangle. - Use the x-axis segment as the base when computing the area.

Solution

1. Factor \(f_k(x)=x(x-k)\). The x-intercepts are \(O=(0,0)\) and \(A=(k,0)\). 2. Differentiate: \(f_k'(x)=2x-k\). The tangent slopes are \(f_k'(0)=-k\) and \(f_k'(k)=k\). 3. The tangent lines are \(y=-kx\) and \(y=k(x-k)=kx-k^2\). 4. Set the equations equal: \(-kx=kx-k^2\). Since \(k>0\), \(x=\frac{k}{2}\). Then \(y=-\frac{k^2}{2}\), so \(S=(\frac{k}{2},-\frac{k^2}{2})\). 5. The base \(OA\) has length \(k\), and the height is \(\frac{k^2}{2}\). Thus, the area is \(\frac{1}{2}\cdot k\cdot\frac{k^2}{2}=\frac{k^3}{4}\). 6. Solve \(\frac{k^3}{4}=16\). This gives \(k^3=64\), so \(k=4\).

Answer

\(k=4\)
52238512
Let \(f(x)=x^2-1\), and let \(Q_a=(a,f(a))\) for \(a\in\mathbb{R}\). The point \(P=(0,-5)\) is also given. a) For \(a\ne 0\), find the slope \(m_a\) of the line through \(P\) and \(Q_a\) in terms of \(a\). b) Let \(t_a\) be the tangent line to the graph of \(f\) at \(Q_a\). Find all real values of \(a\) for which \(t_a\) passes through \(P\).

Hints

- Use the slope formula for two given points. - The derivative at \(a\) gives the tangent slope at \(Q_a\). - Check \(a=0\) separately before using a slope formula that divides by \(a\). - If the tangent passes through \(P\), compare its slope with the slope of \(PQ_a\). - Solve the resulting equation for \(a\).

Solution

1. The slope through \(P=(0,-5)\) and \(Q_a=(a,a^2-1)\) is \(m_a=\frac{(a^2-1)-(-5)}{a-0}=\frac{a^2+4}{a}\). 2. Differentiate: \(f'(x)=2x\), so the tangent slope at \(Q_a\) is \(f'(a)=2a\). 3. If \(a=0\), the tangent line is \(y=-1\), which does not pass through \(P\). For \(a\ne 0\), a tangent line through both \(Q_a\) and \(P\) must have slope \(m_a\). Thus, \(2a=\frac{a^2+4}{a}\). 4. Since \(a\ne 0\), multiply by \(a\): \(2a^2=a^2+4\). Therefore, \(a^2=4\), so \(a=-2\) or \(a=2\).

Answer

a) \(m_a=\frac{a^2+4}{a}\) b) \(a=-2\) and \(a=2\)
52238612
Let \(g(x)=\frac{1}{2}x^3+4\), and let \(S_a=(a,g(a))\). The point \(R=(0,-4)\) is also given. a) For \(a\ne 0\), find the slope \(m_a\) of the line through \(R\) and \(S_a\) in terms of \(a\). b) Let \(t_a\) be the tangent line to the graph of \(g\) at \(x=a\). Find the real value of \(a\) for which \(t_a\) passes through \(R\).

Hints

- Use the slope formula for two points. - The derivative at \(a\) gives the tangent slope. - Check \(a=0\) separately before using a slope formula that divides by \(a\). - If the tangent passes through \(R\), compare its slope with the slope of \(RS_a\). - Solve the resulting equation for \(a\).

Solution

1. Use the slope formula: \(m_a=\frac{(\frac{1}{2}a^3+4)-(-4)}{a-0}=\frac{\frac{1}{2}a^3+8}{a}=\frac{a^3+16}{2a}\). 2. Differentiate: \(g'(x)=\frac{3}{2}x^2\), so the tangent slope at \(x=a\) is \(\frac{3}{2}a^2\). 3. If \(a=0\), the tangent line is \(y=4\), which does not pass through \(R\). For \(a\ne 0\), a tangent line through both \(S_a\) and \(R\) must have slope \(m_a\): \(\frac{3}{2}a^2=\frac{a^3+16}{2a}\). 4. Since \(a\ne 0\), multiply by \(2a\): \(3a^3=a^3+16\). Thus, \(2a^3=16\), so \(a=2\).

Answer

a) \(m_a=\frac{a^3+16}{2a}\) b) \(a=2\)
52598812
For \(k > 0\), consider the family of functions \(f_k(x) = x^3 - kx\). a) Find the positive zero \(x_P\) in terms of \(k\). b) Find the equation of the tangent line \(t_0\) at the origin and the equation of the tangent line \(t_P\) at \(x_P\). c) Show algebraically that the area of the triangle enclosed by the two tangent lines and the x-axis is \(A(k) = \frac{1}{3}k^2\).

Hints

- Treat \(k\) as a constant when differentiating and simplifying. - Use the point-slope form of a tangent line at \(x=x_0\). - For the triangle, find the length of the side on the x-axis and the vertical distance from the third vertex to the x-axis. - Lengths and areas must be positive.

Solution

1. Solve \(x^3 - kx = 0\): \(x(x^2-k)=0\), so the zeros are \(x=0\) and \(x=\pm\sqrt{k}\). Therefore, \(x_P=\sqrt{k}\). 2. Differentiate: \(f_k'(x)=3x^2-k\). 3. At the origin, \(f_k'(0)=-k\). Since the tangent passes through \((0, 0)\), \(t_0: y=-kx\). 4. At \(P(\sqrt{k}, 0)\), the slope is \(f_k'(\sqrt{k})=3k-k=2k\). Thus \(t_P: y=2k(x-\sqrt{k})\). 5. Find the intersection of the tangent lines by solving \(-kx=2k(x-\sqrt{k})\). Since \(k>0\), \(x=\frac{2}{3}\sqrt{k}\), and then \(y=-\frac{2}{3}k\sqrt{k}\). 6. The triangle has base \(\sqrt{k}\) and height \(\frac{2}{3}k\sqrt{k}\). Therefore, \(A(k)=\frac{1}{2}\cdot\sqrt{k}\cdot\frac{2}{3}k\sqrt{k}=\frac{1}{3}k^2\).

Answer

a) \(x_P=\sqrt{k}\) b) \(t_0: y=-kx\); \(t_P: y=2k(x-\sqrt{k})\) c) The tangent lines intersect at \(\left(\frac{2}{3}\sqrt{k}, -\frac{2}{3}k\sqrt{k}\right)\), giving \(A(k)=\frac{1}{3}k^2\).
52900612
Consider \(f(x)=\sqrt{x}\) for \(x>0\). a) Find the general equation of the normal line \(n_a\) at \(x=a\). b) The normal line intersects the x-axis at \(S_x\). Show that the horizontal distance between \(S_x\) and the point of tangency is always \(0.5\), independent of \(a\).

Hints

- Use the normal-line formula at a general input \(a\). - Differentiate the square-root function. - Set \(y=0\) to find the x-intercept. - A constant difference does not depend on \(a\).

Solution

1. Differentiate: \(f'(x)=\frac{1}{2\sqrt{x}}\). 2. At \(x=a\), the normal slope is \(m_n=-\frac{1}{f'(a)}=-2\sqrt{a}\). 3. The normal line is \(y-\sqrt{a}=-2\sqrt{a}(x-a)\). 4. At the x-intercept, \(y=0\): \(0=-2\sqrt{a}(x-a)+\sqrt{a}\). Since \(a>0\), divide by \(\sqrt{a}\) to get \(2(x-a)=1\). 5. Thus, \(x=a+0.5\), and the horizontal distance is \((a+0.5)-a=0.5\).

Answer

a) \(n_a: y=-2\sqrt{a}(x-a)+\sqrt{a}\) b) \(S_x=(a+0.5,0)\), so the horizontal distance is always \(0.5\).
52900912
Let \(f(x)=x^2-2\). Two tangent lines are drawn from the point \(P=(0,-3)\), which is not on the graph. a) Find the points of tangency \(B_1\) and \(B_2\). b) Find equations of both tangent lines in slope-intercept form. c) Find the midpoint \(M\) of \(\overline{B_1B_2}\) and the distance from \(M\) to \(P\).

Hints

- Write the tangent line at an unknown input \(u\). - Require that line to pass through the external point. - Use the midpoint formula after finding both points of tangency. - Points on the same vertical line have distance equal to the difference of their y-coordinates.

Solution

1. A tangent at input \(u\) has equation \(y=f'(u)(x-u)+f(u)\). Since \(f'(x)=2x\), this becomes \(y=2u(x-u)+u^2-2=2ux-u^2-2\). 2. Require the tangent to pass through \(P=(0,-3)\): \(-3=-u^2-2\). Thus, \(u^2=1\), so \(u=-1\) or \(u=1\). 3. The points of tangency are \((-1,-1)\) and \((1,-1)\). 4. For \(u=-1\), the tangent is \(y=-2x-3\). For \(u=1\), the tangent is \(y=2x-3\). 5. The midpoint is \(M=(0,-1)\). Since \(M\) and \(P\) have the same x-coordinate, their distance is \(|-1-(-3)|=2\).

Answer

a) \(B_1=(-1,-1)\) and \(B_2=(1,-1)\) b) \(y=-2x-3\) and \(y=2x-3\) c) \(M=(0,-1)\), and the distance from \(M\) to \(P\) is \(2\).
52901312
Let \(f(x)=x^2\). A normal line at a point \(P(u,v)\) on the graph passes through \(A(0,1.5)\). Find all possible coordinates of \(P\).

Hints

- Relate the tangent and normal slopes at a general point. - Write the normal line at \(x=u\). - Substitute the coordinates of \(A\). - Check separately the case where the tangent is horizontal.

Solution

1. Since \(P\) lies on the graph, \(v=u^2\). Also, \(f'(x)=2x\). 2. For \(u\ne0\), the normal slope is \(-\frac{1}{2u}\), so the normal line is \(y-u^2=-\frac{1}{2u}(x-u)\). 3. Substitute \(A(0,1.5)\): \(1.5-u^2=\frac{1}{2}\). Thus, \(u^2=1\), so \(u=1\) or \(u=-1\). These give \((1,1)\) and \((-1,1)\). 4. Check \(u=0\) separately. The tangent at \((0,0)\) is horizontal, so the normal is the y-axis, which contains \(A\). Therefore, \((0,0)\) is also a solution.

Answer

\((1,1)\), \((-1,1)\), and \((0,0)\)
52901412
Let \(f(x)=\frac{1}{x}\) for \(x\ne0\). A normal line is drawn to the graph at \(x=a\). Find all values of \(a\) for which the normal line passes through the origin \(O(0,0)\). Give the corresponding points \(P(a,f(a))\).

Hints

- Apply the power rule to \(x^{-1}\). - Convert the tangent slope to the normal slope. - Write the normal line at a general input and substitute the origin. - Find all real solutions of \(a^4=1\).

Solution

1. Differentiate: \(f'(x)=-\frac{1}{x^2}\). 2. At \(x=a\), the normal slope is \(m_n=-\frac{1}{f'(a)}=a^2\). 3. The normal line through \(P\left(a,\frac{1}{a}\right)\) is \(y-\frac{1}{a}=a^2(x-a)\). 4. Substitute the origin: \(-\frac{1}{a}=-a^3\), so \(a^4=1\). 5. The real solutions are \(a=1\) and \(a=-1\). The corresponding points are \((1,1)\) and \((-1,-1)\).

Answer

\(a=1\) gives \(P=(1,1)\), and \(a=-1\) gives \(P=(-1,-1)\).
53253612
Let \(f(x)=0.5x^3-1.5x\). The point \(P(2,-3)\) does not lie on the graph of \(f\). Tangent lines drawn from \(P\) touch the graph at points \(Q_a(a,f(a))\), as shown. a) Write the equation of the tangent line \(t_a\) at \(Q_a\) in terms of \(a\). b) Find every value of \(a\) for which \(t_a\) passes through \(P\), and give the equations of those tangent lines.
Figure for problem 532536

Hints

- Use the tangent-line formula at a general input \(a\). - The derivative gives the tangent slope. - Substitute the coordinates of \(P\) into the general tangent equation. - Factor the resulting equation in \(a\).

Solution

1. Differentiate: \(f'(x)=1.5x^2-1.5\). 2. The tangent at \(x=a\) is \(t_a(x)=f'(a)(x-a)+f(a)\). Substitution gives \(t_a(x)=(1.5a^2-1.5)(x-a)+0.5a^3-1.5a\), which simplifies to \(t_a(x)=(1.5a^2-1.5)x-a^3\). 3. Require the tangent to pass through \(P(2,-3)\): \(-3=2(1.5a^2-1.5)-a^3\). This simplifies to \(a^2(3-a)=0\). 4. Therefore, \(a=0\) or \(a=3\). 5. Substitution gives \(t_0(x)=-1.5x\) and \(t_3(x)=12x-27\).

Answer

a) \(t_a(x)=(1.5a^2-1.5)x-a^3\) b) \(a=0\) gives \(t_0(x)=-1.5x\), and \(a=3\) gives \(t_3(x)=12x-27\).
53393412
For \(x>0\), consider the graph of \(f(x)=\frac{1}{x}\). The diagram illustrates the case \(a=2\). a) Find the equation of the tangent line at \(B\left(a,\frac{1}{a}\right)\). b) The tangent line and the coordinate axes form a right triangle. Show algebraically that the area of this triangle is always \(2\), independent of \(a\).
Figure for problem 533934

Hints

- Apply the power rule after writing the reciprocal with a negative exponent. - Find the tangent line's x- and y-intercepts. - The intercepts give the legs of the right triangle. - Check whether \(a\) remains after simplifying the area formula.

Solution

1. Differentiate: \(f'(x)=-\frac{1}{x^2}\). 2. At \(x=a\), the tangent line is \(y=-\frac{1}{a^2}(x-a)+\frac{1}{a}=-\frac{1}{a^2}x+\frac{2}{a}\). 3. Setting \(x=0\) gives the y-intercept \(S_y\left(0,\frac{2}{a}\right)\). 4. Setting \(y=0\) gives \(x=2a\), so the x-intercept is \(S_x(2a,0)\). 5. The triangle has base \(2a\) and height \(\frac{2}{a}\). Its area is \(\frac{1}{2}(2a)\left(\frac{2}{a}\right)=2\), so it is independent of \(a\).

Answer

a) \(y=-\frac{1}{a^2}x+\frac{2}{a}\) b) The intercepts are \(S_x(2a,0)\) and \(S_y\left(0,\frac{2}{a}\right)\), and the area is always \(2\).

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