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Average and instantaneous rate of change

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52223412
Find the slope of the graph of \(f(x)=2x^5-3x^2+10\) at \(x=1\).

Hints

- What does the derivative represent at a point on a graph? - First find the derivative function. - Substitute the given \(x\)-value into the derivative.

Solution

1. Differentiate the function: \(f'(x)=10x^4-6x\). 2. The slope at \(x=1\) is \(f'(1)\). 3. Evaluate: \(f'(1)=10(1)^4-6(1)=4\).

Answer

\(4\)
52223912
Let \(f(x)=\frac{1}{4}x^4-2x^2+3x\). Find the slope of the graph of \(f\) at the point \(P(2, f(2))\).

Hints

- Which quantity gives the slope of a function at a specific input? - Differentiate the function term by term. - Substitute the point's \(x\)-coordinate into the derivative.

Solution

1. Differentiate: \(f'(x)=x^3-4x+3\). 2. Evaluate the derivative at the point's \(x\)-coordinate: \(f'(2)=2^3-4(2)+3=3\).

Answer

The slope at \(P\) is \(3\).
52224012
Find the slope of the tangent line to \(g(x)=\frac{1}{6}x^3+\frac{1}{4}x^2-x\) at \(x=-2\).

Hints

- The slope of the tangent line at \(x=a\) is the derivative value at \(a\). - Differentiate the function term by term. - Use parentheses when substituting a negative value.

Solution

1. Differentiate: \(g'(x)=\frac{1}{2}x^2+\frac{1}{2}x-1\). 2. Evaluate at \(x=-2\): \(g'(-2)=\frac{1}{2}(-2)^2+\frac{1}{2}(-2)-1=0\).

Answer

The slope at \(x=-2\) is \(0\).
52224312
Let \(f(x)=\frac{1}{6}x^3-3x^2+10x\). Find the slope of the graph of \(f\) at \(x=6\).

Hints

- What does the first derivative represent at a point? - Differentiate the polynomial term by term. - Substitute the given input into the derivative.

Solution

1. Differentiate: \(f'(x)=\frac{1}{2}x^2-6x+10\). 2. Evaluate at \(x=6\): \(f'(6)=\frac{1}{2}(6)^2-6(6)+10=-8\).

Answer

The slope at \(x=6\) is \(-8\).
52224412
Find the slope of the tangent line to \(h(x)=0.5x^4-\frac{2}{3}x^3+x-5\) at \(x=-1\).

Hints

- The slope of a tangent line is a derivative value. - Use parentheses when substituting a negative input. - A constant term has derivative \(0\).

Solution

1. Differentiate: \(h'(x)=2x^3-2x^2+1\). 2. Evaluate at \(x=-1\): \(h'(-1)=2(-1)^3-2(-1)^2+1=-3\).

Answer

The tangent line has slope \(-3\) at \(x=-1\).
52224612
Let \(g(x)=-\frac{1}{6}x^6+4x^2-1\). Find \(g'\), and determine algebraically whether the slope of the graph is positive or negative at \(x=-1\).

Hints

- What does the sign of the derivative tell you about the slope of a graph? - Use parentheses when substituting a negative value. - Find the derivative function before evaluating it at the given input.

Solution

1. Differentiate: \(g'(x)=-x^5+8x\). 2. Evaluate at \(x=-1\): \(g'(-1)=-(-1)^5+8(-1)=-7\). 3. Since \(-7<0\), the slope is negative at \(x=-1\).

Answer

\(g'(x)=-x^5+8x\); the slope is negative at \(x=-1\).
52227312
Let \(f(x)=1.5x^2-7x+10\). Find the value of \(x\) for which \(f'(x)=5\).

Hints

- How is a specified slope represented using the derivative? - Differentiate the quadratic function. - Set the derivative equal to the given value. - Solve the resulting equation for \(x\).

Solution

1. Differentiate: \(f'(x)=3x-7\). 2. Set the derivative equal to the required value: \(3x-7=5\). 3. Solve: \(3x=12\), so \(x=4\).

Answer

\(x=4\)
52648912
Let \(f(x)=x^3-3x^2-9x+1\). Use the first derivative to determine whether the graph has positive or negative slope at \(x=-2\) and \(x=2\).

Hints

- Evaluate the first derivative at each given value. - A positive derivative means the graph rises; a negative derivative means it falls.

Solution

1. Differentiate: \(f'(x)=3x^2-6x-9\). 2. At \(x=-2\), \(f'(-2)=3\cdot4-6(-2)-9=15>0\), so the graph has positive slope. 3. At \(x=2\), \(f'(2)=3\cdot4-6\cdot2-9=-9<0\), so the graph has negative slope.

Answer

At \(x=-2\), the slope is positive: \(f'(-2)=15\). At \(x=2\), the slope is negative: \(f'(2)=-9\).
52890312
Find each requested derivative value. a) \(f(x)=x^5\) at \(x=1\), \(x=-2\), and \(x=0\) b) \(g(x)=\frac{2}{x}\) at \(x=2\) and \(x=-4\)

Hints

- Use the power rule to find each derivative function. - Rewrite a variable in the denominator using a negative exponent. - A derivative value gives the graph's slope at that input. - Use parentheses when substituting negative values.

Solution

1. For part a), \(f'(x)=5x^4\). Therefore, \(f'(1)=5\), \(f'(-2)=80\), and \(f'(0)=0\). 2. For part b), rewrite \(g(x)=2x^{-1}\), so \(g'(x)=-2x^{-2}=-\frac{2}{x^2}\). Thus \(g'(2)=-0.5\) and \(g'(-4)=-0.125\).

Answer

a) \(f'(1)=5\), \(f'(-2)=80\), and \(f'(0)=0\) b) \(g'(2)=-0.5\) and \(g'(-4)=-0.125\)
52895112
Let \(f(x)=3\sin x-2\cos x\). Find the slope of the graph at \(x=0\) and at \(x=\frac{\pi}{2}\).

Hints

- Differentiate using the sum and constant multiple rules. - Recall the derivatives of sine and cosine. - Use exact unit-circle values at the two inputs. - The derivative value is the graph’s slope.

Solution

1. Differentiate: \(f'(x)=3\cos x+2\sin x\). 2. At \(x=0\), \(f'(0)=3\). 3. At \(x=\frac{\pi}{2}\), \(f'\left(\frac{\pi}{2}\right)=2\).

Answer

At \(x=0\), the slope is \(3\). At \(x=\frac{\pi}{2}\), the slope is \(2\).
52895212
Let \(h(x)=\sin x+\cos x\). At which inputs in \(\left\{0,\frac{\pi}{2},\pi,\frac{3\pi}{2}\right\}\) does the tangent line have slope \(1\)? Verify your answer algebraically.

Hints

- Differentiate first. - Substitute each candidate input into the derivative. - Use exact unit-circle values. - Select the inputs where the derivative equals \(1\).

Solution

1. Differentiate: \(h'(x)=\cos x-\sin x\). 2. Evaluate at the four inputs: \(h'(0)=1\), \(h'\left(\frac{\pi}{2}\right)=-1\), \(h'(\pi)=-1\), and \(h'\left(\frac{3\pi}{2}\right)=1\). Therefore, the tangent slope is \(1\) at \(x=0\) and \(x=\frac{3\pi}{2}\).

Answer

\(x=0\) and \(x=\frac{3\pi}{2}\)
52895412
For which values of \(x\) does the graph of \(f(x)=x^2-3x+5\) have a tangent line with slope \(0\), \(1\), \(-1\), \(\frac{1}{2}\), or \(-\frac{1}{2}\)?

Hints

- A tangent slope is a value of the derivative. - Find the derivative function first. - Solve one linear equation for each requested slope.

Solution

1. Differentiate: \(f'(x)=2x-3\). 2. Set \(2x-3\) equal to each requested slope and solve. 3. For slope \(0\), \(2x-3=0\), so \(x=1.5\). 4. For slope \(1\), \(2x-3=1\), so \(x=2\). 5. For slope \(-1\), \(2x-3=-1\), so \(x=1\). 6. For slope \(\frac{1}{2}\), \(2x-3=\frac{1}{2}\), so \(x=1.75\). 7. For slope \(-\frac{1}{2}\), \(2x-3=-\frac{1}{2}\), so \(x=1.25\).

Answer

Slope \(0\): \(x=1.5\) Slope \(1\): \(x=2\) Slope \(-1\): \(x=1\) Slope \(\frac{1}{2}\): \(x=1.75\) Slope \(-\frac{1}{2}\): \(x=1.25\)
52896612
Let \(f(x)=x^4-\frac{1}{x^2}\), where \(x\neq0\). a) Find \(f'(x)\). b) Find the slope of the graph at \(x=1\). c) Show algebraically that the graph has negative slope at \(x=-1\).

Hints

- The derivative gives the graph's slope at each input. - Substitute a specified input into the derivative to find the slope there. - Rewrite the reciprocal power using a negative exponent before differentiating. - Use parentheses when substituting negative values.

Solution

1. Rewrite the function as \(f(x)=x^4-x^{-2}\). Then \(f'(x)=4x^3+2x^{-3}=4x^3+\frac{2}{x^3}\). 2. Evaluate: \(f'(1)=4+2=6\). 3. At \(x=-1\), \(f'(-1)=4(-1)^3+\frac{2}{(-1)^3}=-6\). Since \(-6<0\), the slope is negative.

Answer

a) \(f'(x)=4x^3+\frac{2}{x^3}\) b) \(6\) c) \(f'(-1)=-6<0\), so the slope is negative.
52897312
Find every value of \(x\) where each graph has the specified slope. a) \(f(x)=0.5x^2-3x\) with slope \(2\) b) \(g(x)=\frac{2}{x}\), where \(x\neq0\), with slope \(-0.5\)

Hints

- The derivative gives the slope at each input. - Use the power rule for a function with a negative exponent. - Set each derivative equal to the specified slope. - A quadratic equation can have two real solutions.

Solution

1. Differentiate: \(f'(x)=x-3\) and \(g'(x)=-\frac{2}{x^2}\). 2. For part a), solve \(x-3=2\), giving \(x=5\). 3. For part b), solve \(-\frac{2}{x^2}=-0.5\). This gives \(x^2=4\), so \(x=-2\) or \(x=2\).

Answer

a) \(x=5\) b) \(x=-2\) and \(x=2\)
52899012
Let \(f(x)=4\sqrt{x}-\frac{9}{x}+2\), where \(x>0\). a) Find \(f'(x)\). b) Find the slope of the graph at \(x=1\).

Hints

- The derivative value at a point is the graph's slope there. - Rewrite the radical and reciprocal using exponents before differentiating. - After finding the derivative function, substitute the given input.

Solution

1. Rewrite the function as \(f(x)=4x^{1/2}-9x^{-1}+2\). 2. Differentiate: \(f'(x)=2x^{-1/2}+9x^{-2}=\frac{2}{\sqrt{x}}+\frac{9}{x^2}\). 3. Evaluate at \(x=1\): \(f'(1)=2+9=11\).

Answer

a) \(f'(x)=\frac{2}{\sqrt{x}}+\frac{9}{x^2}\), where \(x>0\) b) \(11\)
52944312
Consider the family \(f_k(x)=kx^2+(2-4k)x+4k-3\), where \(k\in\mathbb{R}\). a) Find the point \(P\) that lies on every graph in the family. b) Show that every graph has the same slope at \(P\).

Hints

- Rewrite the expression so that the term containing \(k\) is isolated. - Find the x-value that makes the coefficient of \(k\) equal to zero. - Evaluate the derivative at that x-value.

Solution

1. Rewrite the function as \(f_k(x)=k(x-2)^2+2x-3\). The parameter term is zero when \(x=2\). 2. Then \(f_k(2)=1\), so every graph passes through \(P(2, 1)\). 3. Differentiate: \(f_k'(x)=2kx+2-4k\). At \(x=2\), \(f_k'(2)=4k+2-4k=2\), independent of \(k\). Therefore, every graph has slope \(2\) at \(P\).

Answer

a) \(P(2, 1)\) b) Every graph has slope \(2\) at \(P\).
53368912
The graph shows \(f(x)=0.5x^2-2x\). a) Use derivative rules to find \(f'\). b) Find \(f'(0)\). c) Check your result by using the drawn tangent line to estimate the slope at \(x=0\).
Figure for problem 533689

Hints

- Apply the power rule term by term. - Substitute \(x=0\) into the derivative. - Use two points on the tangent line to compute rise over run.

Solution

1. Differentiate: \(f'(x)=0.5\cdot2x-2=x-2\). 2. Evaluate at \(x=0\): \(f'(0)=0-2=-2\). 3. The tangent line passes through \((0,0)\). Moving \(1\) unit to the right along the line corresponds to moving \(2\) units down, so its slope is \(\frac{-2}{1}=-2\). This agrees with the derivative.

Answer

a) \(f'(x)=x-2\) b) \(f'(0)=-2\) c) The tangent line has slope \(-2\), confirming the calculated value.
53374712
Use the derivative to show algebraically that the graph of \(f(x)=x^3-3x^2+3x\) has a horizontal tangent at \(x=1\).
Figure for problem 533747

Hints

- The derivative gives the slope of the tangent line. - A horizontal line has slope \(0\). - Differentiate first, and then evaluate at \(x=1\).

Solution

1. Differentiate: \(f'(x)=3x^2-6x+3\). 2. Evaluate the derivative at \(x=1\): \(f'(1)=3-6+3=0\). 3. Because the tangent slope is \(0\), the tangent line is horizontal at \(x=1\).

Answer

\(f'(x)=3x^2-6x+3\) and \(f'(1)=0\), so the tangent line is horizontal at \(x=1\).
53417512
For \(f(x)=2x^2-3x\), use derivative rules to find the instantaneous rate of change at \(x=1\).
Figure for problem 534175

Hints

- Apply the power rule to each term. - Keep constant factors when differentiating. - Evaluate the derivative at \(x=1\).

Solution

1. Differentiate using the power rule: \(f'(x)=4x-3\). 2. Evaluate the derivative: \(f'(1)=4-3=1\). 3. The instantaneous rate of change at \(x=1\) is \(1\).

Answer

\(f'(1)=1\)
53417612
Let \(g(x)=x^3-4x^2+2\). Find the slope of the graph at \(x=2\).
Figure for problem 534176

Hints

- Differentiate each term separately. - The derivative of a constant is \(0\). - Substitute \(x=2\) after differentiating.

Solution

1. Differentiate: \(g'(x)=3x^2-8x\). 2. Evaluate at \(x=2\): \(g'(2)=3\cdot2^2-8\cdot2=12-16=-4\). 3. The graph has slope \(-4\) at \(x=2\).

Answer

\(g'(2)=-4\)
52225912
Find the slope of the graph of \(f(x)=x^4-5x^3+4x^2\) at every point where the graph intersects either coordinate axis.

Hints

- Find the y-intercept by setting \(x=0\). - Find the x-intercepts by solving \(f(x)=0\). - The slope at an intercept is the derivative evaluated at that intercept's \(x\)-coordinate. - Be sure to evaluate the derivative at every distinct intercept input.

Solution

1. Differentiate: \(f'(x)=4x^3-15x^2+8x\). 2. The graph intersects the y-axis at \((0,0)\). 3. Factor to find the x-intercepts: \(f(x)=x^2(x^2-5x+4)=x^2(x-1)(x-4)\). Thus the distinct intercept inputs are \(x=0\), \(x=1\), and \(x=4\). 4. Evaluate the derivative: \(f'(0)=0\), \(f'(1)=-3\), and \(f'(4)=48\).

Answer

At \((0,0)\), the slope is \(0\). At \((1,0)\), the slope is \(-3\). At \((4,0)\), the slope is \(48\).
52226012
Let \(g(x)=0.5x^2-2x-6\). Find the slope of the tangent line at each x-intercept and at the y-intercept of the graph.

Hints

- First find the coordinates of all intercepts. - Differentiate the function to obtain its slope function. - Check the signs carefully when solving the quadratic equation. - Substitute each intercept's \(x\)-coordinate into the derivative.

Solution

1. Differentiate: \(g'(x)=x-2\). 2. The y-intercept is \((0,-6)\), and \(g'(0)=-2\). 3. To find the x-intercepts, solve \(0.5x^2-2x-6=0\). Multiplying by \(2\) gives \(x^2-4x-12=0=(x-6)(x+2)\), so \(x=6\) or \(x=-2\). 4. Evaluate the derivative: \(g'(6)=4\) and \(g'(-2)=-4\).

Answer

At the y-intercept \((0,-6)\), the slope is \(-2\). At the x-intercepts \((6,0)\) and \((-2,0)\), the slopes are \(4\) and \(-4\), respectively.
52227412
Let \(f(x)=\frac{1}{3}x^3+\frac{1}{2}x^2-4x+5\). Find every value of \(x\) where the tangent line to the graph of \(f\) is parallel to \(y=8x-1\).

Hints

- Parallel lines have equal slopes. - Which coefficient in slope-intercept form gives the slope? - The derivative gives the tangent slope at each input. - After setting the derivative equal to the line's slope, solve the resulting quadratic equation.

Solution

1. The line \(y=8x-1\) has slope \(8\). 2. Differentiate: \(f'(x)=x^2+x-4\). 3. Parallel tangent lines must have slope \(8\), so solve \(x^2+x-4=8\). 4. This gives \(x^2+x-12=0=(x+4)(x-3)\). 5. Therefore, \(x=-4\) or \(x=3\).

Answer

\(x=-4\) and \(x=3\)
52227512
Let \(f(x)=x^2-4x+5\) and \(g(x)=\frac{1}{3}x^3-2x^2+x\). a) Find the value of \(x\) where the graph of \(f\) has slope \(6\). b) Determine whether the graph of \(g\) has the same slope at the value found in part a). c) Find every other value of \(x\) where the graphs of \(f\) and \(g\) have the same slope.

Hints

- The derivative gives the slope at a specific input. - Set a derivative equal to a required slope to form an equation. - Equal slopes at the same input mean the derivative values are equal. - Set the two derivative functions equal and solve for \(x\).

Solution

1. Differentiate: \(f'(x)=2x-4\) and \(g'(x)=x^2-4x+1\). 2. For part a), solve \(2x-4=6\), giving \(x=5\). 3. For part b), \(g'(5)=25-20+1=6\), so both graphs have slope \(6\) at \(x=5\). 4. For part c), set the derivatives equal: \(2x-4=x^2-4x+1\). 5. Rearranging gives \(x^2-6x+5=0=(x-1)(x-5)\). The solutions are \(x=1\) and \(x=5\), so the additional value is \(x=1\).

Answer

a) \(x=5\) b) Yes. Both graphs have slope \(6\) at \(x=5\). c) The other value is \(x=1\).
52227612
Let \(h(x)=x^3-6x^2+9x+2\). a) Find the coordinates of every point on the graph of \(h\) where the tangent line is horizontal. b) Let \(k(x)=-1.5x^2+3x+5\). Find every value of \(x\) where the graphs of \(h\) and \(k\) have the same slope.

Hints

- What is the slope of a horizontal line? - After finding an \(x\)-coordinate, substitute it into the original function to find the point. - If two graphs have the same slope at the same input, their derivatives are equal there. - Solve the resulting quadratic equations by factoring or another valid method.

Solution

1. Differentiate: \(h'(x)=3x^2-12x+9\) and \(k'(x)=-3x+3\). 2. For part a), horizontal tangent lines have slope \(0\), so solve \(3x^2-12x+9=0\). 3. Dividing by \(3\) gives \(x^2-4x+3=0=(x-1)(x-3)\), so \(x=1\) or \(x=3\). 4. Evaluate the function: \(h(1)=6\) and \(h(3)=2\). The points are \((1,6)\) and \((3,2)\). 5. For part b), set the derivatives equal: \(3x^2-12x+9=-3x+3\). 6. Simplifying gives \(x^2-3x+2=0=(x-1)(x-2)\), so \(x=1\) or \(x=2\).

Answer

a) \((1,6)\) and \((3,2)\) b) \(x=1\) and \(x=2\)
52611712
Consider the family of functions \(f_k(x)=ke^x-x\), where \(k\in\mathbb{R}\setminus\{0\}\). a) Find \(f_k'(x)\). b) The tangent line at \(x=0\) passes through \((2, 5)\). Find \(k\).

Hints

- Use the point-slope form of a tangent line. - Find both the function value and derivative value at \(x=0\). - A point on the tangent line must satisfy its equation. - Express the tangent slope and y-intercept in terms of \(k\).

Solution

1. Differentiate: \(f_k'(x)=ke^x-1\). 2. At \(x=0\), \(f_k(0)=k\) and \(f_k'(0)=k-1\). 3. The tangent line is \(y=(k-1)x+k\). 4. Substitute \((2, 5)\): \(5=2(k-1)+k\). 5. Solve \(5=3k-2\) to obtain \(k=\frac{7}{3}\).

Answer

a) \(f_k'(x)=ke^x-1\) b) \(k=\frac{7}{3}\)
52613212
Consider the family of functions \(g_a(x)=ae^{x-1}+2\), where \(a\in\mathbb{R}\setminus\{0\}\). a) Find the equation of the tangent line at \((1, g_a(1))\). b) Find all values of \(a\) for which this tangent has positive slope and crosses the x-axis at an x-coordinate greater than \(-1\).

Hints

- Find both the function value and slope at \(x=1\). - Simplify the tangent equation before applying the conditions. - Positive slope determines the sign of \(a\). - Set the tangent equation equal to \(0\) to find its x-intercept. - Translate the x-intercept condition into an inequality for \(a\).

Solution

1. At \(x=1\), \(g_a(1)=a+2\). 2. Differentiate: \(g_a'(x)=ae^{x-1}\), so the tangent slope at \(x=1\) is \(a\). 3. The tangent line is \(y-(a+2)=a(x-1)\), which simplifies to \(y=ax+2\). 4. Positive slope requires \(a>0\). 5. The x-intercept is \(x=-\frac{2}{a}\). Require \(-\frac{2}{a}>-1\). 6. Since \(a>0\), multiplication by \(a\) preserves the inequality: \(-2>-a\), so \(a>2\).

Answer

a) \(y=ax+2\) b) \(a>2\)
52639812
The family of functions \(f_k\) is defined by \(f_k(x)=kx^3-3x^2+5\), where \(k\in\mathbb{R}\). a) Find the derivative function \(f_k'(x)\). b) Find the value of \(k\) for which the graph of \(f_k\) has a horizontal tangent at \(x=1\).

Hints

- A horizontal tangent has slope \(0\). - Treat the parameter \(k\) as a constant when differentiating with respect to \(x\). - Substitute the specified input into the derivative before solving for \(k\).

Solution

1. Treat \(k\) as a constant and differentiate: \(f_k'(x)=3kx^2-6x\). 2. A horizontal tangent has slope \(0\), so require \(f_k'(1)=0\). 3. Substitute \(x=1\): \(3k-6=0\). 4. Solving gives \(k=2\).

Answer

a) \(f_k'(x)=3kx^2-6x\) b) \(k=2\)
52640212
Let \(f(x)=\frac{1}{3}x^3-x^2-5x+2\). Find every value of \(x\) where the graph of \(f\) has slope \(3\).

Hints

- The derivative gives the slope at each input. - What value must the derivative equal at the requested points? - Solve the resulting quadratic equation. - Check that you found every solution.

Solution

1. Differentiate: \(f'(x)=x^2-2x-5\). 2. Set the derivative equal to the required slope: \(x^2-2x-5=3\). 3. Rearrange: \(x^2-2x-8=0\). 4. Factor: \((x-4)(x+2)=0\). 5. Therefore, \(x=4\) or \(x=-2\).

Answer

\(x=-2\) and \(x=4\)
52761212
Consider the family \(f_k(x)=\frac{x+k}{x}\), where \(k>0\) and \(x\neq 0\). Show that for every \(k\), there is a tangent line to the graph of \(f_k\) that passes through the origin. Find the point of tangency \(B\).

Hints

- Rewrite the function before differentiating. - Write the tangent line at a general x-coordinate \(x_0\). - Use the fact that the origin lies on the tangent line. - Substitute the resulting x-coordinate into the original function.

Solution

1. Rewrite the function as \(f_k(x)=1+\frac{k}{x}\), so \(f_k'(x)=-\frac{k}{x^2}\). 2. Let the point of tangency have x-coordinate \(x_0\). The tangent line is \(y=f_k'(x_0)(x-x_0)+f_k(x_0)\). 3. Since the line passes through \((0, 0)\), \(0=-\frac{k}{x_0^2}(0-x_0)+1+\frac{k}{x_0}\). 4. Simplify: \(0=1+\frac{2k}{x_0}\), so \(x_0=-2k\). Since \(k>0\), this is a valid domain value. 5. The y-coordinate is \(f_k(-2k)=\frac{-2k+k}{-2k}=\frac{1}{2}\). Therefore, \(B=\left(-2k, \frac{1}{2}\right)\).

Answer

\(B=\left(-2k, \frac{1}{2}\right)\)
52890712
Let \(f(x)=x^3+3x\). 1) Find \(f'(x)\). 2) Determine which tangent-slope values \(m\) cannot occur on the graph of \(f\). 3) Interpret the result geometrically.

Hints

- Tangent slopes are the values of the first derivative. - Find the minimum value of \(3x^2+3\). - Interpret a derivative that is always positive.

Solution

1. Differentiate: \(f'(x)=3x^2+3\). 2. Since \(x^2\ge0\), \(f'(x)\ge3\) for every real \(x\). Therefore, the possible slopes are \([3,\infty)\), and every slope \(m<3\) is impossible. 3. Geometrically, the graph is strictly increasing everywhere. It has no horizontal or negative-slope tangent, and its smallest slope is \(3\) at \(x=0\).

Answer

1) \(f'(x)=3x^2+3\) 2) Every slope \(m<3\) is impossible. 3) The graph rises everywhere, and its minimum tangent slope is \(3\) at \(x=0\).
52890812
Let \(g(x)=-\frac{1}{x^2}\), where \(x\ne0\). Analyze the possible signs of the tangent slope for \(x<0\) and \(x>0\). Which slope values are excluded altogether? Interpret the result geometrically.

Hints

- Rewrite the function with a negative exponent. - Determine the sign of \(x^3\) on each side of zero. - A fraction with a nonzero constant numerator cannot equal zero.

Solution

1. Rewrite and differentiate: \(g(x)=-x^{-2}\), so \(g'(x)=2x^{-3}=\frac{2}{x^3}\). 2. For \(x<0\), \(x^3<0\), so \(g'(x)<0\). The left branch is strictly decreasing. 3. For \(x>0\), \(x^3>0\), so \(g'(x)>0\). The right branch is strictly increasing. 4. The derivative can never equal zero because its numerator is the nonzero constant \(2\). Every nonzero real slope occurs, but \(m=0\) is excluded. 5. Geometrically, neither branch has a horizontal tangent.

Answer

For \(x<0\), slopes are negative. For \(x>0\), slopes are positive. The only excluded slope is \(m=0\).
52895312
Let \(f(x)=\frac{1}{3}x^3-\frac{1}{4}x\). For which values of \(x\) does \(f'(x)\) equal each of the following values? \(0\), \(\frac{3}{4}\), and \(2\)

Hints

- First find the derivative function. - Set the derivative equal to each required value. - Solve each resulting equation for \(x\). - An equation of the form \(x^2=a\) can have two real solutions.

Solution

1. Differentiate: \(f'(x)=x^2-\frac{1}{4}\). 2. For \(f'(x)=0\), solve \(x^2=\frac{1}{4}\), giving \(x=\pm\frac{1}{2}\). 3. For \(f'(x)=\frac{3}{4}\), solve \(x^2=1\), giving \(x=\pm1\). 4. For \(f'(x)=2\), solve \(x^2=\frac{9}{4}\), giving \(x=\pm\frac{3}{2}\).

Answer

For \(f'(x)=0\): \(x\in\left\{-\frac{1}{2},\frac{1}{2}\right\}\) For \(f'(x)=\frac{3}{4}\): \(x\in\{-1,1\}\) For \(f'(x)=2\): \(x\in\left\{-\frac{3}{2},\frac{3}{2}\right\}\)
52895712
Let \(f(x)=x^3+3x+2\). Explain algebraically why no tangent line to the graph of \(f\) has slope \(2\).

Hints

- Which function gives the tangent slope at each input? - Set the derivative equal to the proposed slope. - What values can the square of a real number take?

Solution

1. Differentiate: \(f'(x)=3x^2+3\). 2. A tangent line with slope \(2\) would require \(3x^2+3=2\). 3. This equation simplifies to \(x^2=-\frac{1}{3}\), which has no real solution. 4. Equivalently, since \(x^2\geq0\), \(f'(x)=3x^2+3\geq3\) for every real \(x\).

Answer

\(f'(x)=3x^2+3\geq3\) for every \(x\in\mathbb{R}\), so the derivative never equals \(2\).
52895812
Let \(g(x)=4\cos x\). Which real numbers cannot occur as tangent slopes to the graph? State your answer using inequalities.

Hints

- Find the derivative. - Use the range of sine. - Account for the constant factor and negative sign. - Report the values outside the derivative’s range.

Solution

1. Differentiate: \(g'(x)=-4\sin x\). 2. Since \(-1\le\sin x\le 1\), the derivative satisfies \(-4\le g'(x)\le 4\). Therefore, tangent slopes outside this interval cannot occur.

Answer

The impossible slopes are \(m<-4\) or \(m>4\).
52903212
The graph of \(g(x)=ax^2+4x-2\), where \(a\in\mathbb{R}\), has a tangent line with slope \(2\) at \(x=-1\). a) Find \(a\). b) Find an equation of the tangent line.

Hints

- The tangent slope at \(x=-1\) is \(g'(-1)\). - Use the given slope to form an equation containing only \(a\). - Find the point of tangency after determining \(a\). - Use the point-slope form of a line.

Solution

1. Differentiate: \(g'(x)=2ax+4\). 2. Use the given slope: \(g'(-1)=2\). Therefore, \(-2a+4=2\), so \(a=1\). 3. With \(a=1\), the point of tangency is \((-1,g(-1))=(-1,-5)\). 4. A line with slope \(2\) through \((-1,-5)\) satisfies \(y+5=2(x+1)\), so \(y=2x-3\).

Answer

a) \(a=1\) b) \(y=2x-3\)
52931612
Find all cubic polynomials that are symmetric about the origin and have slope \(6\) at \(x=1\). Which one also passes through \(Q(2, 20)\)?

Hints

- Use only odd powers for origin symmetry. - Translate the slope condition into an equation involving the derivative. - Leave one coefficient as a parameter when finding all possible functions. - Use the additional point to determine the parameter.

Solution

1. A cubic polynomial symmetric about the origin has the form \(f(x)=ax^3+cx\), where \(a\ne0\). 2. Since \(f'(x)=3ax^2+c\), the slope condition \(f'(1)=6\) gives \(3a+c=6\), so \(c=6-3a\). 3. Therefore, all such cubic polynomials are \(f_a(x)=ax^3+(6-3a)x\), where \(a\in\mathbb{R}\setminus\{0\}\). 4. To pass through \(Q(2, 20)\), the polynomial must satisfy \(8a+2(6-3a)=20\). Thus, \(2a+12=20\), so \(a=4\) and \(c=-6\). 5. The required polynomial is \(f(x)=4x^3-6x\).

Answer

All such polynomials: \(f_a(x)=ax^3+(6-3a)x\), where \(a\in\mathbb{R}\setminus\{0\}\) Polynomial through \(Q(2, 20)\): \(f(x)=4x^3-6x\)
52935412
Find a cubic polynomial whose graph passes through the origin and \(P(2, 4)\), and is tangent to the x-axis at \(x=4\).

Hints

- Tangency to the x-axis gives both a zero and a zero slope. - Use the origin to determine the constant term. - Translate each remaining condition into an equation. - Solve the resulting linear system.

Solution

1. Let \(f(x)=ax^3+bx^2+cx+d\). Passing through the origin gives \(d=0\). 2. The point \(P(2, 4)\) gives \(8a+4b+2c=4\). Tangency to the x-axis at \(x=4\) gives \(f(4)=0\) and \(f'(4)=0\), so \(64a+16b+4c=0\) and \(48a+8b+c=0\). 3. Solving the system gives \(a=\frac{1}{2}\), \(b=-4\), and \(c=8\). 4. Therefore, \(f(x)=\frac{1}{2}x^3-4x^2+8x\).

Answer

\(f(x)=\frac{1}{2}x^3-4x^2+8x\)
52994812
Let \(h(x)=\log_bx\), where \(b>0\) and \(b\ne1\). For what value of \(b\) does the graph have slope \(0.5\) at \(x=2\)?

Hints

- Recall the derivative of \(\log_bx\). - Substitute the given input and slope. - Solve the resulting equation for \(\ln b\). - Exponentiate to solve for \(b\).

Solution

1. Differentiate: \(h'(x)=\frac{1}{x\ln b}\). 2. Use the given slope: \(\frac{1}{2\ln b}=0.5=\frac{1}{2}\). Therefore, \(\ln b=1\), so \(b=e\).

Answer

\(b=e\)
53009812
Let \(f(x)=\frac{ax^2+bx}{x-2}\). a) Find \(a\) and \(b\) so that the graph has a horizontal tangent at \(x=0\) and passes through \(P(4, 8)\). b) For those parameter values, show that the graph has a slant asymptote and give its equation. Also describe the one-sided behavior near the vertical asymptote.

Hints

- Use the given point to form one parameter equation. - A horizontal tangent means the first derivative is zero. - Use polynomial division after finding the parameters. - Check the signs of the numerator and denominator on each side of the vertical asymptote.

Solution

1. The point condition gives \(f(4)=8\): \(\frac{16a+4b}{2}=8\), so \(4a+b=4\). 2. Differentiate: \(f'(x)=\frac{(2ax+b)(x-2)-(ax^2+bx)}{(x-2)^2}=\frac{ax^2-4ax-2b}{(x-2)^2}\). 3. A horizontal tangent at \(x=0\) requires \(f'(0)=0\), so \(b=0\). Then \(4a=4\), giving \(a=1\). 4. The function is \(f(x)=\frac{x^2}{x-2}=x+2+\frac{4}{x-2}\). Therefore, the slant asymptote is \(y=x+2\). 5. The vertical asymptote is \(x=2\). Since the numerator is positive near \(2\), \(\lim_{x\to 2^-}f(x)=-\infty\) and \(\lim_{x\to 2^+}f(x)=\infty\).

Answer

a) \(a=1\), \(b=0\) b) Slant asymptote: \(y=x+2\); \(\lim_{x\to 2^-}f(x)=-\infty\) and \(\lim_{x\to 2^+}f(x)=\infty\)
53017312
Find \(a\), \(b\), and \(c\) so that \(f(x)=a\sin x+b\cos(2x)+c\) has y-intercept \(4\), passes through \(\left(\frac{\pi}{2}, 1\right)\), and has slope \(2\) at \(x=0\).

Hints

- Convert each graph condition into an equation involving \(f\) or \(f'\). - Differentiate the general function before using the slope condition. - Use exact sine and cosine values at \(0\), \(\frac{\pi}{2}\), and \(\pi\). - Solve the resulting linear system for the three parameters.

Solution

1. Translate the conditions into equations: \(f(0)=4\), \(f\left(\frac{\pi}{2}\right)=1\), and \(f'(0)=2\). 2. Differentiate: \(f'(x)=a\cos x-2b\sin(2x)\). From \(f'(0)=2\), \(a=2\). 3. From \(f(0)=4\), \(b+c=4\). 4. From \(f\left(\frac{\pi}{2}\right)=1\), \(2-b+c=1\), so \(-b+c=-1\). 5. Solve the system \(b+c=4\) and \(-b+c=-1\). This gives \(b=\frac{5}{2}\) and \(c=\frac{3}{2}\).

Answer

\(a=2\), \(b=\frac{5}{2}\), and \(c=\frac{3}{2}\) Therefore, \(f(x)=2\sin x+\frac{5}{2}\cos(2x)+\frac{3}{2}\).
53267012
a) Let \(h(x)=\ln(3x-5)\). Find its maximal domain, its zero, and \(h'(x)\). b) A differentiable function \(f\) is defined for all real \(x\), has its only zero at \(x=-2\), and satisfies \(f'(x)>0\) for every real \(x\). Its graph is shown. Define \(g(x)=\ln(f(x))\). 1. Find the maximal domain of \(g\). 2. Use the graph to find the input where \(g'(x)=\frac{1}{2}f'(x)\).
Figure for problem 532670

Hints

- A logarithm requires a positive argument. - Apply the chain rule to \(\ln(u(x))\). - Use the monotonicity and zero of \(f\) to determine where \(f(x)>0\). - Express \(g'\) in terms of \(f\) and \(f'\), then simplify the equation. - Read the required function value from the graph.

Solution

1. For part a, require \(3x-5>0\), so \(D_h=\left(\frac{5}{3}, \infty\right)\). The zero satisfies \(3x-5=1\), giving \(x=2\). By the chain rule, \(h'(x)=\frac{3}{3x-5}\). 2. Since \(f\) is strictly increasing and has its only zero at \(-2\), \(f(x)>0\) exactly when \(x>-2\). Therefore, \(D_g=(-2, \infty)\). Also, \(g'(x)=\frac{f'(x)}{f(x)}\). The equation \(\frac{f'(x)}{f(x)}=\frac{1}{2}f'(x)\) can be divided by \(f'(x)>0\), giving \(f(x)=2\). From the graph, \(f(x)=2\) at \(x=2\).

Answer

a) \(D_h=\left(\frac{5}{3}, \infty\right)\), zero at \(x=2\), and \(h'(x)=\frac{3}{3x-5}\) b) 1. \(D_g=(-2, \infty)\) 2. \(x=2\)
53392512
Let \(f(x)=\frac{1}{4}x^3\) and \(g(x)=x\). a) Find all points where the two graphs intersect. b) Find the acute angle of intersection at each point.
Figure for problem 533925

Hints

- Substitute each point into both functions. - Differentiate to find the tangent slopes. - Use the acute-angle formula for two lines with known slopes. - At the origin, one tangent is horizontal.

Solution

1. Set the functions equal: \(\frac{1}{4}x^3=x\). Then \(x(x^2-4)=0\), so \(x=-2\), \(x=0\), or \(x=2\). The intersection points are \(Q(-2,-2)\), \(O(0,0)\), and \(P(2,2)\). 2. The tangent slopes are given by \(f'(x)=\frac{3}{4}x^2\) and \(g'(x)=1\). 3. At \(O\), the slopes are \(0\) and \(1\), so the acute angle is \(45^\circ\). 4. At both \(Q\) and \(P\), the slopes are \(3\) and \(1\). Thus, \(\tan\theta=\left|\frac{3-1}{1+3\cdot1}\right|=\frac{1}{2}\), so \(\theta=\arctan(\frac{1}{2})\approx26.6^\circ\).

Answer

a) \(Q(-2,-2)\), \(O(0,0)\), and \(P(2,2)\) b) At \(O\), the acute angle is \(45^\circ\). At \(Q\) and \(P\), it is \(\arctan(\frac{1}{2})\approx26.6^\circ\).
53422512
Let \(f(x)=x^2-2x-1\). a) Find \(f'\). b) Find the point \(P\) on the graph of \(f\) where the tangent line has slope \(2\). c) Find the point \(Q\) where the tangent line to the graph of \(f\) is parallel to \(y=-4x+5\).
Figure for problem 534225

Hints

- Use the power rule to find the derivative. - The derivative value is the tangent slope. - Parallel lines have equal slopes. - Substitute each x-value into \(f\) to find the point's y-coordinate.

Solution

1. Differentiate: \(f'(x)=2x-2\). 2. For slope \(2\), solve \(2x-2=2\), giving \(x=2\). Then \(f(2)=-1\), so \(P=(2,-1)\). 3. A line parallel to \(y=-4x+5\) has slope \(-4\). Solve \(2x-2=-4\), giving \(x=-1\). Then \(f(-1)=2\), so \(Q=(-1,2)\).

Answer

a) \(f'(x)=2x-2\) b) \(P=(2,-1)\) c) \(Q=(-1,2)\)
53422612
Let \(f(x)=-0.5x^2+3x\). a) Find \(f'\). b) Find the point \(S\) where the graph of \(f\) has a horizontal tangent. c) At what x-value is the tangent line parallel to \(y=x\)? Give the corresponding point \(R\).
Figure for problem 534226

Hints

- Differentiate each term. - A horizontal tangent has slope \(0\). - Parallel lines have the same slope; \(y=x\) has slope \(1\). - Substitute each x-value into \(f\) to find the corresponding point.

Solution

1. Differentiate: \(f'(x)=-x+3\). 2. For a horizontal tangent, solve \(-x+3=0\), giving \(x=3\). Since \(f(3)=4.5\), \(S=(3,4.5)\). 3. The line \(y=x\) has slope \(1\). Solve \(-x+3=1\), giving \(x=2\). Since \(f(2)=4\), \(R=(2,4)\).

Answer

a) \(f'(x)=-x+3\) b) \(S=(3,4.5)\) c) \(x=2\), and \(R=(2,4)\)
53442912
The graph shows \(f(x)=x+1.5\sin x\), \(g(x)=x\), and \(h(x)=1.5\sin x\). a) Explain the shape of the graph of \(f\) using the graphs of \(g\) and \(h\). b) Use the graph to estimate, and then calculate, all inputs in \([0, 2\pi]\) where the tangent to the graph of \(f\) is parallel to the line \(g\). c) Explain without further differentiation why \(f(x)\) cannot be negative when \(x>0\).
Figure for problem 534429

Hints

- Add the y-values of the two component functions. - Parallel lines have equal slopes. - Look for where the cosine term in the derivative is zero. - Use \(-1\le\sin x\le1\) to bound \(f(x)\).

Solution

1. Since \(f(x)=g(x)+h(x)\), the graph of \(f\) is obtained by adding the y-values of the line \(y=x\) and the sine curve \(y=1.5\sin x\). Thus, it oscillates around the line \(y=x\). 2. The line \(g(x)=x\) has slope \(1\). Differentiate: \(f'(x)=1+1.5\cos x\). Parallel tangents satisfy \(1+1.5\cos x=1\), so \(\cos x=0\). On \([0, 2\pi]\), this occurs at \(x=\frac{\pi}{2}\) and \(x=\frac{3\pi}{2}\). 3. For \(0<x\le\pi\), \(\sin x\ge0\), so \(f(x)>0\). For \(x>\pi\), \(f(x)=x+1.5\sin x\ge x-1.5>\pi-1.5>0\). Therefore, \(f(x)>0\) for all \(x>0\).

Answer

a) The graph of \(f\) is the pointwise sum of the graphs of \(g\) and \(h\), so it oscillates around \(y=x\). b) \(x=\frac{\pi}{2}\) and \(x=\frac{3\pi}{2}\) c) For \(0<x\le\pi\), both terms are nonnegative. For \(x>\pi\), \(f(x)\ge x-1.5>0\).
53443012
The graph shows \(f(x)=0.5x-\cos x\), \(g(x)=0.5x\), and \(h(x)=-\cos x\). a) Identify the graph of each function. b) Find the coordinates of all points on the graph of \(f\) in \([0, 2\pi]\) where the slope is \(0.5\). c) Determine whether the graph of \(f\) has horizontal tangents. Give all such inputs if they exist.
Figure for problem 534430

Hints

- Compare the shapes and formulas of the three functions. - Set the derivative equal to the desired slope in part b. - A horizontal tangent requires the derivative to equal zero. - Use the unit circle to solve the resulting sine equations.

Solution

1. The line through the origin is \(g(x)=0.5x\), the reflected cosine curve is \(h(x)=-\cos x\), and their pointwise sum is \(f(x)=0.5x-\cos x\). 2. Differentiate: \(f'(x)=0.5+\sin x\). For slope \(0.5\), solve \(0.5+\sin x=0.5\), so \(\sin x=0\). On \([0, 2\pi]\), the inputs are \(0\), \(\pi\), and \(2\pi\). The corresponding points are \((0, -1)\), \(\left(\pi, \frac{\pi}{2}+1\right)\), and \((2\pi, \pi-1)\). 3. Horizontal tangents satisfy \(0.5+\sin x=0\), so \(\sin x=-\frac{1}{2}\). Therefore, \(x=\frac{7\pi}{6}+2\pi n\) or \(x=\frac{11\pi}{6}+2\pi n\), where \(n\in\mathbb{Z}\).

Answer

a) \(g\) is the line through the origin, \(h\) is the reflected cosine curve, and \(f\) is their sum. b) \((0, -1)\), \(\left(\pi, \frac{\pi}{2}+1\right)\), and \((2\pi, \pi-1)\) c) \(x=\frac{7\pi}{6}+2\pi n\) or \(x=\frac{11\pi}{6}+2\pi n\), where \(n\in\mathbb{Z}\)
52625412
Consider the family of functions \(f_{a,k}(x)=(x+a)e^{kx}\), where \(a\in\mathbb{R}\) and \(k\in\mathbb{R}\setminus\{0\}\). A graph has y-intercept \((0, 3)\). Its tangent line at that point makes a \(45^\circ\) angle with the y-axis. Find \(a\) and \(k\).

Hints

- Use the y-intercept to determine \(a\). - A \(45^\circ\) angle with the y-axis corresponds to slopes \(1\) or \(-1\). - The derivative at the y-intercept gives the tangent slope. - Apply the restriction \(k\neq0\).

Solution

1. The y-intercept gives \(f_{a,k}(0)=a=3\). 2. Differentiate: \(f_{a,k}'(x)=(1+kx+ak)e^{kx}\). 3. At \(x=0\), the tangent slope is \(1+3k\). 4. A line making a \(45^\circ\) angle with the y-axis has slope \(1\) or \(-1\). 5. The equation \(1+3k=1\) gives \(k=0\), which is excluded. The equation \(1+3k=-1\) gives \(k=-\frac{2}{3}\). 6. Therefore, \(a=3\) and \(k=-\frac{2}{3}\).

Answer

\(a=3\) and \(k=-\frac{2}{3}\)
52897412
For \(n\in\{1,2,3,4,5,6\}\), let \(f_n(x)=x^n\). Determine which values of \(n\) make \(f_n\) have exactly two real inputs where the tangent slope is \(10\).

Hints

- Differentiate the general function \(f_n(x)=x^n\). - How many real solutions can \(x^k=c\), with \(c>0\), have when \(k\) is even or odd? - Connect the parity of the exponent in the derivative to the number of solutions. - Check \(n=1\) separately.

Solution

1. Differentiate: \(f_n'(x)=nx^{n-1}\). The slope condition is \(nx^{n-1}=10\), or \(x^{n-1}=\frac{10}{n}\). 2. Since \(\frac{10}{n}>0\), the equation has exactly two real solutions when the positive exponent \(n-1\) is even. 3. The case \(n=1\) must be checked separately: \(f_1'(x)=1\), so there are no solutions. 4. For \(n=3\), \(x^2=\frac{10}{3}\) has two solutions. For \(n=5\), \(x^4=2\) has two solutions. 5. For \(n=2,4,6\), the exponent \(n-1\) is odd, so each equation has exactly one real solution.

Answer

\(n=3\) and \(n=5\)

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