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Chain rule

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52583112
Find the derivative of \(h(z)=\frac{1}{4}(2z^3+5)^4\).

Hints

- Identify the inner function and the outer power function. - Use the chain rule: outer derivative times inner derivative. - Include the constant factor \(\frac{1}{4}\) when differentiating the outer function.

Solution

1. Let the inner function be \(u(z)=2z^3+5\). Then \(u'(z)=6z^2\). 2. The outer function is \(\frac{1}{4}u^4\), whose derivative with respect to \(u\) is \(u^3\). 3. Apply the chain rule: \(h'(z)=(2z^3+5)^3(6z^2)\) \(=6z^2(2z^3+5)^3\).

Answer

\(h'(z)=6z^2(2z^3+5)^3\)
52583212
Find the derivative of \(k(t)=2\sin(4t^2-\pi)+t^2\).

Hints

- Differentiate the two terms separately. - The sine term is a composite function. - What is the derivative of the expression inside the sine? - Multiply by the inner derivative when applying the chain rule.

Solution

1. Differentiate the two terms separately. 2. For the sine term, the inner function is \(u(t)=4t^2-\pi\), with \(u'(t)=8t\). By the chain rule, \(\frac{d}{dt}[2\sin(4t^2-\pi)]=2\cos(4t^2-\pi)(8t)\) \(=16t\cos(4t^2-\pi)\). 3. Also, \(\frac{d}{dt}(t^2)=2t\). Therefore, \(k'(t)=16t\cos(4t^2-\pi)+2t\).

Answer

\(k'(t)=16t\cos(4t^2-\pi)+2t\)
52584812
A student differentiates \(f(x)=\sin^2(5x)\) as follows: Step 1: \(f(x)=(\sin(5x))^2\) Step 2: \(f'(x)=2\sin(5x)\cos(5x)\) Describe the error in Step 2 and find the correct derivative.

Hints

- Count the layers of composition from the outside inward. - Each layer should contribute a factor to the derivative. - What is the innermost function, and what is its derivative? - Rewriting the function with parentheses can make the layers clearer.

Solution

1. The function has three layers: the square, the sine function, and the inner linear function \(5x\). 2. The student differentiated the square and the sine but did not multiply by the derivative of \(5x\). 3. Applying the chain rule through all layers gives \(f'(x)=2\sin(5x)\cos(5x)\cdot 5\) \(=10\sin(5x)\cos(5x)\).

Answer

The derivative of the innermost function \(5x\) was omitted. The correct derivative is \(f'(x)=10\sin(5x)\cos(5x)\).
52586512
Find the derivative value at the indicated input. a) \(f(x)=(2x-5)^4\) at \(x=3\) b) \(g(t)=\sqrt{t^2+7}\) at \(t=3\)

Hints

- Identify the inner and outer functions. - Use the chain rule for each composite function. - Multiply by the derivative of the inner function. - Find the general derivative before substituting the given input.

Solution

1. For a), apply the chain rule: \(f'(x)=4(2x-5)^3\cdot 2=8(2x-5)^3\). Therefore, \(f'(3)=8 \cdot (6-5)^3=8\). 2. For b), \(g'(t)=\frac{1}{2\sqrt{t^2+7}}(2t)=\frac{t}{\sqrt{t^2+7}}\). Therefore, \(g'(3)=\frac{3}{\sqrt{16}}=\frac{3}{4}\).

Answer

a) \(f'(3)=8\) b) \(g'(3)=\frac{3}{4}\)
52587312
Let \(f(x)=(2x^3+7)^5\). a) Give an outer function \(u\) and an inner function \(v\) such that \(f(x)=u(v(x))\). b) Find \(u'(x)\) and \(v'(x)\). c) Find \(u'(v(x))\), then use the chain rule to find \(f'(x)\).

Hints

- The operation performed last is usually the outer function. - Identify the expression inside the outer power. - When differentiating the outer function, temporarily keep the inner input unchanged.

Solution

1. Choose \(u(x)=x^5\) and \(v(x)=2x^3+7\). 2. Their derivatives are \(u'(x)=5x^4\) and \(v'(x)=6x^2\). 3. Substitute \(v(x)\) into \(u'\): \(u'(v(x))=5(2x^3+7)^4\). 4. By the chain rule, \(f'(x)=u'(v(x))v'(x)\) \(=5(2x^3+7)^4(6x^2)\) \(=30x^2(2x^3+7)^4\).

Answer

a) \(u(x)=x^5\); \(v(x)=2x^3+7\) b) \(u'(x)=5x^4\); \(v'(x)=6x^2\) c) \(u'(v(x))=5(2x^3+7)^4\); \(f'(x)=30x^2(2x^3+7)^4\)
52587912
Find the derivative of \(f(x)=\frac{1}{2}(2x^3-4)^5\).

Hints

- Identify the inner and outer functions. - Use the rule “outer derivative times inner derivative.” - Differentiate the power while keeping the inner expression unchanged. - What is the derivative of the expression inside the parentheses?

Solution

1. Let the inner function be \(v(x)=2x^3-4\), so \(v'(x)=6x^2\). 2. The derivative of the outer function \(\frac{1}{2}v^5\) is \(\frac{5}{2}v^4\). 3. Apply the chain rule: \(f'(x)=\frac{5}{2}(2x^3-4)^4(6x^2)\) \(=15x^2(2x^3-4)^4\).

Answer

\(f'(x)=15x^2(2x^3-4)^4\)
52590312
Use the chain rule to justify that the derivative of \(f(x)=e^{\sin(x)}\) is \(f'(x)=\cos(x)e^{\sin(x)}\).

Hints

- Identify which function is applied first and which is applied second. - Recall the chain rule for a composition. - Differentiate the outer and inner functions separately. - Multiply the outer derivative evaluated at the inner function by the inner derivative.

Solution

1. Let the outer function be \(u(v)=e^v\) and the inner function be \(v(x)=\sin(x)\). 2. Their derivatives are \(u'(v)=e^v\) and \(v'(x)=\cos(x)\). 3. By the chain rule, \(f'(x)=u'(v(x))v'(x)\) \(=e^{\sin(x)}\cos(x)\), which is the stated expression.

Answer

With \(u(v)=e^v\) and \(v(x)=\sin(x)\), the chain rule gives \(f'(x)=e^{\sin(x)}\cos(x)\).
52590412
Consider the function \(g(x)=\ln(\cos(x))\) on the interval \(\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)\). Use the chain rule to justify that \(g'(x)=-\tan(x)\).

Hints

- Identify the inner and outer functions. - Recall the derivatives of the natural logarithm and cosine. - Pay attention to the sign when differentiating the inner function. - Use a trigonometric identity to simplify the quotient.

Solution

1. Let the outer function be \(u(v)=\ln(v)\) and the inner function be \(v(x)=\cos(x)\). 2. Their derivatives are \(u'(v)=\frac{1}{v}\) and \(v'(x)=-\sin(x)\). 3. By the chain rule, \(g'(x)=u'(v(x))v'(x)\) \(=\frac{1}{\cos(x)}(-\sin(x))\) \(=-\frac{\sin(x)}{\cos(x)}=-\tan(x)\).

Answer

The chain rule gives \(g'(x)=\frac{1}{\cos(x)}(-\sin(x))=-\tan(x)\).
52593912
Write each function as a composition \(f(x)=u(v(x))\) by identifying suitable inner and outer functions. Then find \(f'(x)\). a) \(f(x)=(2x^2-1)^6\) b) \(f(x)=4\sqrt{x^3+2}\)

Hints

- Identify the operation performed last; it is usually the outer function. - Look for the expression inside the parentheses or under the radical. - Use the chain rule: derivative of the outer function times derivative of the inner function. - Rewriting a square root as a fractional power may help.

Solution

1. For a), choose \(u(t)=t^6\) and \(v(x)=2x^2-1\). Then \(u'(t)=6t^5\) and \(v'(x)=4x\). By the chain rule, \(f'(x)=6(2x^2-1)^5(4x)=24x(2x^2-1)^5\). 2. For b), choose \(u(t)=4\sqrt{t}\) and \(v(x)=x^3+2\). Then \(u'(t)=\frac{2}{\sqrt{t}}\) and \(v'(x)=3x^2\). By the chain rule, \(f'(x)=\frac{2}{\sqrt{x^3+2}}(3x^2)=\frac{6x^2}{\sqrt{x^3+2}}\). This derivative is defined for \(x>-\sqrt[3]{2}\).

Answer

a) \(u(t)=t^6\), \(v(x)=2x^2-1\); \(f'(x)=24x(2x^2-1)^5\) b) \(u(t)=4\sqrt{t}\), \(v(x)=x^3+2\); \(f'(x)=\frac{6x^2}{\sqrt{x^3+2}}\) for \(x>-\sqrt[3]{2}\)
52594012
Write each function as a composition \(f(x)=u(v(x))\) by identifying suitable inner and outer functions. Then find \(f'(x)\). a) \(f(x)=\cos(2x^4-x)\) b) \(f(x)=(\sin(x)-5)^2\)

Hints

- Identify the expression used as the input to the trigonometric function or power. - In a), keep the entire derivative of the inner function together. - Ask what operation is performed first and what operation is performed afterward. - Remember the negative sign in the derivative of cosine.

Solution

1. For a), choose \(u(t)=\cos(t)\) and \(v(x)=2x^4-x\). Since \(u'(t)=-\sin(t)\) and \(v'(x)=8x^3-1\), the chain rule gives \(f'(x)=-\sin(2x^4-x)(8x^3-1)\) \(=(1-8x^3)\sin(2x^4-x)\). 2. For b), choose \(u(t)=t^2\) and \(v(x)=\sin(x)-5\). Since \(u'(t)=2t\) and \(v'(x)=\cos(x)\), the chain rule gives \(f'(x)=2(\sin(x)-5)\cos(x)\).

Answer

a) \(u(t)=\cos(t)\), \(v(x)=2x^4-x\); \(f'(x)=(1-8x^3)\sin(2x^4-x)\) b) \(u(t)=t^2\), \(v(x)=\sin(x)-5\); \(f'(x)=2(\sin(x)-5)\cos(x)\)
52613712
Use the chain rule to find the derivative of each function. a) \(f(x)=e^{4x-2}\) b) \(g(x)=5e^{-0.2x}\) c) \(h(x)=e^{x^2+3}\) d) \(k(x)=\frac{1}{e^{2x}}\)

Hints

- Identify the expression inside each exponent. - Differentiate the outer exponential function, then multiply by the derivative of the exponent. - Keep constant factors. - Rewrite a reciprocal exponential using a negative exponent.

Solution

1. For \(f(x)=e^{4x-2}\), the inner derivative is \(4\), so \(f'(x)=4e^{4x-2}\). 2. For \(g(x)=5e^{-0.2x}\), multiply by the inner derivative \(-0.2\): \(g'(x)=5\cdot(-0.2)e^{-0.2x}=-e^{-0.2x}\). 3. For \(h(x)=e^{x^2+3}\), the inner derivative is \(2x\), so \(h'(x)=2xe^{x^2+3}\). 4. Rewrite \(k(x)=e^{-2x}\). Then \(k'(x)=-2e^{-2x}=-\frac{2}{e^{2x}}\).

Answer

a) \(f'(x)=4e^{4x-2}\) b) \(g'(x)=-e^{-0.2x}\) c) \(h'(x)=2xe^{x^2+3}\) d) \(k'(x)=-2e^{-2x}=-\frac{2}{e^{2x}}\)
52645312
Use the chain rule to find the derivative of each function. 1) \(f(x)=\sin(4x)\) 2) \(f(x)=5\cos(2x-1)\) 3) \(f(x)=\sin(0.5x)+\cos(x^2)\)

Hints

- Identify the inner and outer functions in each term. - Multiply by the derivative of the inner function when applying the chain rule. - Remember the negative sign in the derivative of cosine.

Solution

1. For \(f(x)=\sin(4x)\), differentiate the outer sine function and multiply by the derivative of \(4x\): \(f'(x)=\cos(4x)\cdot 4=4\cos(4x)\). 2. For \(f(x)=5\cos(2x-1)\), \(f'(x)=5[-\sin(2x-1)]\cdot 2=-10\sin(2x-1)\). 3. Differentiate each term: \(\frac{d}{dx}\sin(0.5x)=0.5\cos(0.5x)\) and \(\frac{d}{dx}\cos(x^2)=-2x\sin(x^2)\). Therefore, \(f'(x)=0.5\cos(0.5x)-2x\sin(x^2)\).

Answer

1) \(f'(x)=4\cos(4x)\) 2) \(f'(x)=-10\sin(2x-1)\) 3) \(f'(x)=0.5\cos(0.5x)-2x\sin(x^2)\)
52646012
Consider the functions \(u(x)=\sin^2(x)\) and \(v(x)=-\cos^2(x)\). a) Find \(u'(x)\) and \(v'(x)\). b) Compare the derivatives. Use the Pythagorean identity \(\sin^2(x)+\cos^2(x)=1\) to explain why this result is expected.

Hints

- First differentiate both functions using the chain rule. - Recall the derivatives of sine and cosine, including the sign. - Solve the Pythagorean identity for \(\sin^2(x)\). - Consider how adding a constant affects a derivative.

Solution

1. Apply the chain rule to \(u(x)=(\sin(x))^2\): \(u'(x)=2\sin(x)\cos(x)=\sin(2x)\). 2. Apply the chain rule to \(v(x)=-(\cos(x))^2\): \(v'(x)=-2\cos(x)(-\sin(x))=2\sin(x)\cos(x)=\sin(2x)\). 3. Thus, \(u'(x)=v'(x)\). 4. The Pythagorean identity gives \(\sin^2(x)=1-\cos^2(x)\), so \(u(x)=v(x)+1\). Functions that differ by a constant have the same derivative.

Answer

a) \(u'(x)=\sin(2x)\) and \(v'(x)=\sin(2x)\) b) The derivatives are equal because \(u(x)=v(x)+1\), so the functions differ only by a constant.
52757412
Let \(g(t)=\frac{10}{\sqrt{t^2+4}}\), with its largest real domain \(D\). Find \(D\) and \(g'(t)\).

Hints

- Determine whether the radical or denominator can ever be zero. - Rewrite a radical denominator using a negative rational exponent. - Apply the chain rule to the composite power. - Multiply by the derivative of \(t^2+4\).

Solution

1. Since \(t^2+4\ge4\) for every real \(t\), the radical is positive and the denominator is never zero. Thus, \(D=\mathbb{R}\). 2. Rewrite \(g(t)=10(t^2+4)^{-\frac{1}{2}}\). 3. Apply the chain rule: \(g'(t)=10\left(-\frac{1}{2}\right)(t^2+4)^{-\frac{3}{2}}(2t)=-\frac{10t}{(t^2+4)^{\frac{3}{2}}}\).

Answer

\(D=\mathbb{R}\); \(g'(t)=-\frac{10t}{(t^2+4)^{\frac{3}{2}}}\)
52762112
Let \(f(x)=\ln(x^2+4x)\) on the interval \(x>0\). Find \(f'(x)\) and state the domain of the derivative within this interval.

Hints

- Identify the inner function inside the logarithm. - Differentiate the outer and inner functions. - Combine them using the chain rule. - Check whether the denominator can be zero when \(x>0\).

Solution

1. Apply the chain rule with inner function \(v(x)=x^2+4x\): \(f'(x)=\frac{v'(x)}{v(x)}=\frac{2x+4}{x^2+4x}\). 2. For every \(x>0\), the denominator \(x^2+4x=x(x+4)\) is positive. Therefore, the derivative is defined throughout the stated interval.

Answer

\(f'(x)=\frac{2x+4}{x^2+4x}\), with domain \((0, \infty)\)
52765212
Let \(g(x)=\ln(2x+e)\), where \(x>-\frac{e}{2}\). Find the exact zero of \(g\) and find \(g'(x)\).

Hints

- The natural logarithm equals zero when its input equals \(1\). - Solve the resulting linear equation. - Apply the chain rule to the logarithm.

Solution

1. Solve \(\ln(2x+e)=0\). Then \(2x+e=1\), so \(x=\frac{1-e}{2}\). 2. Apply the chain rule: \(g'(x)=\frac{2}{2x+e}\).

Answer

Zero: \(x=\frac{1-e}{2}\) \(g'(x)=\frac{2}{2x+e}\)
52951312
Let \(f(x)=(2x^3-5)^2\). Find \(f'(x)\) in two ways. 1) Differentiate directly using the chain rule. 2) Expand the expression first, and then differentiate term by term. Compare the two results.

Hints

- Identify the inner and outer functions for the chain-rule method. - Use the square of a difference to expand the expression. - Expand the chain-rule result before comparing the two answers.

Solution

1. Using the chain rule, \(f'(x)=2(2x^3-5)(6x^2)\) \(=12x^2(2x^3-5)=24x^5-60x^2\). 2. Expanding first gives \(f(x)=4x^6-20x^3+25\). Differentiating term by term, \(f'(x)=24x^5-60x^2\). Both methods give the same derivative.

Answer

\(f'(x)=24x^5-60x^2\)
52951712
Consider compositions of functions in differentiation. a) Let \(g(x)=mx+c\) and \(k(x)=ax+b\). Show algebraically that \(L(x)=(g\circ k)(x)\) is also linear, and state its slope. b) Let \(f(x)=x^2\). Use the chain rule to find the derivative of \(h(x)=(f\circ g)(x)\). c) Use your results from a) and b) to explain why the derivative of a composition of a quadratic function with a linear function must be linear.

Hints

- A linear function can be written in the form \(y=px+q\). - Substitute the entire formula for the inner function into the outer function. - Use the chain rule: outer derivative times inner derivative. - Multiplying a linear function by a constant still gives a linear function.

Solution

1. For a), substitute \(k(x)\) into \(g\): \(L(x)=m(ax+b)+c=max+mb+c\). This is linear, with slope \(ma\). 2. For b), \(h(x)=(mx+c)^2\). By the chain rule, \(h'(x)=2(mx+c)m=2m^2x+2mc\). 3. The derivative of the outer quadratic function is linear. Composing that linear derivative with the inner linear function produces another linear function, as shown in a). Multiplying by the constant inner derivative \(m\) preserves linearity. Therefore, \(h'\) is linear.

Answer

a) \(L(x)=max+mb+c\), so its slope is \(ma\). b) \(h'(x)=2m(mx+c)=2m^2x+2mc\) c) The derivative is a constant multiple of a composition of two linear functions, so it is linear.
52951912
Use the chain rule to find the derivative of each function. a) \(f(x)=\sin(x^2+3)\) b) \(f(x)=\sqrt{10-2x}\) c) \(f(x)=0.5\cos(4x)\)

Hints

- Identify the inner and outer functions. - Apply the rule “outer derivative times inner derivative.” - Pay close attention to signs, especially for cosine and the decreasing linear expression under the square root.

Solution

1. For a), \(f'(x)=\cos(x^2+3)(2x)=2x\cos(x^2+3)\). 2. For b), \(f'(x)=\frac{1}{2\sqrt{10-2x}}\cdot(-2)=-\frac{1}{\sqrt{10-2x}}\). This derivative is defined for \(x<5\). 3. For c), \(f'(x)=0.5[-\sin(4x)]\cdot 4=-2\sin(4x)\).

Answer

a) \(f'(x)=2x\cos(x^2+3)\) b) \(f'(x)=-\frac{1}{\sqrt{10-2x}}\) for \(x<5\) c) \(f'(x)=-2\sin(4x)\)
53459412
Let \(f(x)=\ln(6-2x)\), with its maximal domain. Find the \(x\)-intercept of \(f\) and a formula for \(f'(x)\).
Figure for problem 534594

Hints

- A natural logarithm equals \(0\) when its input equals \(1\). - Use the chain rule for \(\ln(u(x))\). - Simplify the derivative after applying the rule.

Solution

1. For the \(x\)-intercept, solve \(\ln(6-2x)=0\). Then \(6-2x=1\), so \(x=\frac{5}{2}\). The intercept is \(\left(\frac{5}{2}, 0\right)\). 2. By the chain rule, \(f'(x)=\frac{-2}{6-2x}=\frac{1}{x-3}\).

Answer

\(x\)-intercept: \(\left(\frac{5}{2}, 0\right)\); \(f'(x)=\frac{1}{x-3}\)
52582812
A student differentiates \(g(x)=(2x^3-5)^4\) and writes \(g'(x)=4(2x^3-5)^3\). Explain the error, find the correct derivative, and use it to find the slope of the graph at \(x=1\).

Hints

- The chain rule requires multiplying by the derivative of the inner function. - Differentiate the expression inside the parentheses separately. - Evaluate the derivative at the specified \(x\)-value to find the slope. - Track the sign when raising a negative number to an odd power.

Solution

1. The student differentiated the outer fourth power but omitted the derivative of the inner function. 2. The inner function is \(u(x)=2x^3-5\), with \(u'(x)=6x^2\). 3. By the chain rule, \(g'(x)=4(2x^3-5)^3(6x^2)\) \(=24x^2(2x^3-5)^3\). 4. Evaluate at \(x=1\): \(g'(1)=24 \cdot 1^2 \cdot (2-5)^3=24 \cdot (-3)^3=-648\).

Answer

The inner derivative was omitted. The correct derivative is \(g'(x)=24x^2(2x^3-5)^3\), and the slope at \(x=1\) is \(-648\).
52584712
Each derivative below is incorrect. Explain the error and give the correct derivative. a) \(f(x)=(x^5-2)^4\), with the incorrect derivative \(f'(x)=4(x^5-2)^3\) b) \(g(x)=\cos(3x^2)\), with the incorrect derivative \(g'(x)=-6x\sin(6x)\) c) \(h(x)=e^{4x+1}\), with the incorrect derivative \(h'(x)=4e^4\)

Hints

- The chain rule has the form “outer derivative times inner derivative.” - Keep the original inner expression as the input of the differentiated outer function. - For an exponential function, check whether the original exponent has been preserved. - Look for factors that should have appeared from differentiating the inner function.

Solution

1. In a), the inner derivative is missing. Since \(\frac{d}{dx}(x^5-2)=5x^4\), \(f'(x)=4(x^5-2)^3(5x^4)=20x^4(x^5-2)^3\). 2. In b), the derivative of the inner function was incorrectly substituted into the sine argument. The original inner expression remains inside the outer derivative: \(g'(x)=-\sin(3x^2)(6x)=-6x\sin(3x^2)\). 3. In c), the exponent was incorrectly changed. For \(e^{u(x)}\), the exponential factor remains \(e^{u(x)}\): \(h'(x)=e^{4x+1}(4)=4e^{4x+1}\).

Answer

a) The inner derivative was omitted. \(f'(x)=20x^4(x^5-2)^3\). b) The argument of the sine function was changed incorrectly. \(g'(x)=-6x\sin(3x^2)\). c) The exponent was changed incorrectly. \(h'(x)=4e^{4x+1}\).
52586612
Find the value of the first derivative at the indicated input. a) \(f(x)=e^{x^2-1}\) at \(x=1\) b) \(g(x)=\sin^2(x)\) at \(x=\frac{\pi}{4}\)

Hints

- Recall the derivative of an exponential function and the basic trigonometric functions. - Rewrite \(\sin^2(x)\) as \((\sin(x))^2\) to see the composition. - You may simplify \(2\sin(x)\cos(x)\) using a double-angle identity.

Solution

1. For a), apply the chain rule: \(f'(x)=e^{x^2-1}(2x)\). Therefore, \(f'(1)=e^0 \cdot 2=2\). 2. For b), write \(g(x)=(\sin(x))^2\). Then \(g'(x)=2\sin(x)\cos(x)\). At \(x=\frac{\pi}{4}\), \(g'\left(\frac{\pi}{4}\right)=2 \cdot \left(\frac{\sqrt{2}}{2}\right) \cdot \left(\frac{\sqrt{2}}{2}\right)=1\).

Answer

a) \(f'(1)=2\) b) \(g'\left(\frac{\pi}{4}\right)=1\)
52587412
Let \(f(x)=e^{\cos(x)}\). a) Give functions \(u\) and \(v\) such that \(f=u\circ v\). b) Find \(u'(x)\), \(v'(x)\), and \(u'(v(x))\). c) Find \(f'(x)\). d) Find the slope of the graph of \(f\) at \(x=\frac{\pi}{2}\).

Hints

- Recall the derivative of the natural exponential function. - What sign appears when cosine is differentiated? - A slope at a point is found by evaluating the derivative there. - Use the unit-circle values of sine and cosine at \(\frac{\pi}{2}\).

Solution

1. Choose \(u(x)=e^x\) and \(v(x)=\cos(x)\). 2. Then \(u'(x)=e^x\), \(v'(x)=-\sin(x)\), and \(u'(v(x))=e^{\cos(x)}\). 3. By the chain rule, \(f'(x)=u'(v(x))v'(x)\) \(=-\sin(x)e^{\cos(x)}\). 4. At \(x=\frac{\pi}{2}\), \(f'\left(\frac{\pi}{2}\right)=-\sin\left(\frac{\pi}{2}\right)e^{\cos(\frac{\pi}{2})}\) \(=-1\cdot e^0=-1\).

Answer

a) \(u(x)=e^x\); \(v(x)=\cos(x)\) b) \(u'(x)=e^x\); \(v'(x)=-\sin(x)\); \(u'(v(x))=e^{\cos(x)}\) c) \(f'(x)=-\sin(x)e^{\cos(x)}\) d) \(f'\left(\frac{\pi}{2}\right)=-1\)
52588012
For \(t\ne\frac{2}{3}\), find the derivative of \(g(t)=3\cos(2t^2+5)-\frac{4}{3t-2}\).

Hints

- Differentiate the two terms separately. - Rewrite the rational term using a negative exponent. - Identify the inner function in the cosine term. - Watch the negative sign when differentiating cosine. - Apply the chain rule to both terms.

Solution

1. Differentiate the first term using the chain rule: \(\frac{d}{dt}[3\cos(2t^2+5)]=-3\sin(2t^2+5)(4t)\) \(=-12t\sin(2t^2+5)\). 2. Rewrite the second term as \(-4(3t-2)^{-1}\). Then \(\frac{d}{dt}[-4(3t-2)^{-1}]=4(3t-2)^{-2}\cdot 3\) \(=\frac{12}{(3t-2)^2}\). 3. Combine the results: \(g'(t)=-12t\sin(2t^2+5)+\frac{12}{(3t-2)^2}\).

Answer

\(g'(t)=-12t\sin(2t^2+5)+\frac{12}{(3t-2)^2}\), for \(t\ne\frac{2}{3}\)
52588312
Find each derivative. All parameters are real numbers. a) \(f_k(x)=(kx^2-5)^4\) b) \(g_a(t)=\sin(at-a)\) c) \(h_b(x)=\cos^2(bx)\)

Hints

- Distinguish the variable from the parameters in each function. - Identify the inner and outer functions. - Watch the sign when differentiating cosine. - Make the power structure explicit before applying the chain rule.

Solution

1. For a), apply the chain rule: \(f_k'(x)=4(kx^2-5)^3(2kx)\) \(=8kx(kx^2-5)^3\). 2. For b), \(g_a'(t)=\cos(at-a)(a)\) \(=a\cos(at-a)\). 3. For c), write \(h_b(x)=(\cos(bx))^2\). Applying the chain rule through both layers gives \(h_b'(x)=2\cos(bx)[-b\sin(bx)]\) \(=-2b\sin(bx)\cos(bx)\).

Answer

a) \(f_k'(x)=8kx(kx^2-5)^3\) b) \(g_a'(t)=a\cos(at-a)\) c) \(h_b'(x)=-2b\sin(bx)\cos(bx)\)
52588412
Find each derivative. The parameters \(a\), \(c\), and \(k\) are real. a) \(f_c(z)=\sin(cz^3)\) b) \(g_a(x)=\cos((ax)^2)\) c) \(h_{a,k}(t)=t\sin(ak^2)\)

Hints

- Check which variable each function is differentiated with respect to. - Any expression that does not contain the variable acts like a constant. - For composite functions, differentiate the inner function separately. - Simplify an inner expression before differentiating when helpful.

Solution

1. For a), the inner function is \(cz^3\), whose derivative is \(3cz^2\). Therefore, \(f_c'(z)=3cz^2\cos(cz^3)\). 2. For b), \((ax)^2=a^2x^2\), whose derivative with respect to \(x\) is \(2a^2x\). Thus, \(g_a'(x)=-2a^2x\sin(a^2x^2)\). 3. For c), \(t\) is the variable and \(\sin(ak^2)\) is a constant factor. Therefore, \(h_{a,k}'(t)=\sin(ak^2)\).

Answer

a) \(f_c'(z)=3cz^2\cos(cz^3)\) b) \(g_a'(x)=-2a^2x\sin(a^2x^2)\) c) \(h_{a,k}'(t)=\sin(ak^2)\)
52589312
Let \(f(x)=\frac{1}{2}(0.5x+1)^4\). a) Find the slope of the graph at \(x=2\). b) Determine whether the graph has any points with horizontal tangent lines. If so, find them. c) Find the point where the tangent line makes an angle of \(45^\circ\) with the positive x-axis.

Hints

- Use the chain rule for a power of a linear expression. - A horizontal tangent has derivative \(0\). - Convert the given angle to a slope. - Find the y-coordinate after solving for the x-coordinate.

Solution

1. Differentiate using the chain rule: \(f'(x)=\frac{1}{2}\cdot 4(0.5x+1)^3\cdot 0.5=(0.5x+1)^3\). 2. At \(x=2\), \(f'(2)=(2)^3=8\). 3. A horizontal tangent has slope \(0\). Solve \((0.5x+1)^3=0\), giving \(x=-2\). Since \(f(-2)=0\), the point is \((-2,0)\). 4. An angle of \(45^\circ\) corresponds to slope \(1\). Solve \((0.5x+1)^3=1\), giving \(x=0\). 5. Since \(f(0)=\frac{1}{2}\), the point is \((0,\frac{1}{2})\).

Answer

a) \(8\) b) Yes; the point is \((-2,0)\). c) \((0,\frac{1}{2})\)
52589412
Let \(f(x)=\frac{1}{3}(2-x)^3\). a) Find an equation of the tangent line at \(x=1\). b) Find the point where the graph has a horizontal tangent line. c) Find all points where the tangent line makes an angle of \(135^\circ\), measured counterclockwise from the positive x-axis.

Hints

- Use the chain rule and track the sign of the inner derivative. - A horizontal tangent has slope \(0\). - Convert \(135^\circ\) to a slope. - A squared equation may have two solutions.

Solution

1. Differentiate using the chain rule: \(f'(x)=-(2-x)^2\). 2. At \(x=1\), \(f(1)=\frac{1}{3}\) and \(f'(1)=-1\). The tangent line is \(y-\frac{1}{3}=-(x-1)\), or \(y=-x+\frac{4}{3}\). 3. A horizontal tangent has slope \(0\). Solve \(-(2-x)^2=0\), giving \(x=2\). Since \(f(2)=0\), the point is \((2,0)\). 4. An angle of \(135^\circ\) corresponds to slope \(-1\). Solve \(-(2-x)^2=-1\), so \((2-x)^2=1\). Thus, \(x=1\) or \(x=3\). 5. The corresponding points are \((1,\frac{1}{3})\) and \((3,-\frac{1}{3})\).

Answer

a) \(y=-x+\frac{4}{3}\) b) \((2,0)\) c) \((1,\frac{1}{3})\) and \((3,-\frac{1}{3})\)
52590712
Let \(f\) be differentiable. Find \(g'(x)\) in terms of \(f\) and \(f'\). Assume each function is differentiable on its domain. a) \(g(x)=f(e^x)\) b) \(g(x)=(f(x)+k)^3\), where \(k\in\mathbb{R}\) c) \(g(x)=f\left(\frac{1}{x}\right)\), where \(x\ne 0\) d) \(g(x)=\sqrt{f(x)}\), where \(f(x)>0\)

Hints

- For each part, identify the inner and outer functions. - Use the chain rule: differentiate the outer function, then multiply by the derivative of the inner function. - In b), remember how constants behave under differentiation. - Rewriting a reciprocal or square root as a power may help.

Solution

1. For a), the inner function is \(e^x\), whose derivative is \(e^x\). Therefore, \(g'(x)=e^x f'(e^x)\). 2. For b), apply the chain rule to the outer function \(u^3\) and the inner function \(f(x)+k\): \(g'(x)=3(f(x)+k)^2f'(x)\). 3. For c), the inner function is \(x^{-1}\), whose derivative is \(-x^{-2}\). Therefore, \(g'(x)=-\frac{1}{x^2}f'\left(\frac{1}{x}\right)\). 4. For d), differentiate the outer function \(\sqrt{u}\) and multiply by the derivative of the inner function: \(g'(x)=\frac{f'(x)}{2\sqrt{f(x)}}\).

Answer

a) \(g'(x)=e^x f'(e^x)\) b) \(g'(x)=3(f(x)+k)^2f'(x)\) c) \(g'(x)=-\frac{1}{x^2}f'\left(\frac{1}{x}\right)\) d) \(g'(x)=\frac{f'(x)}{2\sqrt{f(x)}}\)
52590812
Let \(f\) be differentiable. Find \(g'(x)\) in terms of \(f'\). a) \(g(x)=f(ax^n+b)\), where \(a,b\in\mathbb{R}\) and \(n\) is a positive integer b) \(g(x)=\frac{1}{n}(f(x))^n\), where \(n\) is a positive integer c) \(g(x)=f(f(x))\) d) \(g(x)=af(bx+c)+d\), where \(a,b,c,d\in\mathbb{R}\)

Hints

- Treat \(a\), \(b\), \(c\), and \(d\) as constants. - Identify the inner and outer functions in each composition. - Apply the power rule together with the chain rule. - For \(f(f(x))\), distinguish the derivative of the outer copy of \(f\) from the derivative of the inner copy.

Solution

1. For a), the derivative of the inner function \(ax^n+b\) is \(anx^{n-1}\). Thus, \(g'(x)=anx^{n-1}f'(ax^n+b)\). 2. For b), differentiate the outer function \(\frac{1}{n}u^n\), then multiply by \(f'(x)\): \(g'(x)=(f(x))^{n-1}f'(x)\). 3. For c), the outer copy of \(f\) is evaluated at \(f(x)\), while the inner derivative is \(f'(x)\). Therefore, \(g'(x)=f'(f(x))f'(x)\). 4. For d), the constant \(d\) differentiates to zero, the factor \(a\) remains, and the inner linear function has derivative \(b\). Therefore, \(g'(x)=abf'(bx+c)\).

Answer

a) \(g'(x)=anx^{n-1}f'(ax^n+b)\) b) \(g'(x)=(f(x))^{n-1}f'(x)\) c) \(g'(x)=f'(f(x))f'(x)\) d) \(g'(x)=abf'(bx+c)\)
52592712
Let \(f\) be differentiable, and define \(g(x)=f(x^2)\). a) Show that the graph of \(g\) is symmetric about the y-axis. b) Use the chain rule to find \(g'(x)\). c) Show algebraically that the graph of \(g'\) is symmetric about the origin.

Hints

- What equation characterizes a function whose graph is symmetric about the y-axis? - Use the chain rule for a function of the form \(f(u(x))\). - What equation characterizes a function whose graph is symmetric about the origin? - When substituting \(-x\) into \(g'(x)\), track the sign of the linear factor carefully.

Solution

1. For a), \(g(-x)=f((-x)^2)=f(x^2)=g(x)\). Therefore, \(g\) is even, so its graph is symmetric about the y-axis. 2. For b), apply the chain rule: \(g'(x)=f'(x^2)(2x)=2x f'(x^2)\). 3. For c), \(g'(-x)=2(-x)f'((-x)^2)\) \(=-2x f'(x^2)=-g'(x)\). Therefore, \(g'\) is odd, so its graph is symmetric about the origin.

Answer

a) Since \(g(-x)=f((-x)^2)=f(x^2)=g(x)\), the graph of \(g\) is symmetric about the y-axis. b) \(g'(x)=2x f'(x^2)\) c) Since \(g'(-x)=-2x f'(x^2)=-g'(x)\), the graph of \(g'\) is symmetric about the origin.
52594112
Let \(f(x)=e^{\cos(2x+1)}\). a) Give formulas for functions \(u\), \(v\), and \(w\) such that \(f=u\circ v\circ w\). b) Find \(f'(x)\) by applying the chain rule twice.

Hints

- Identify the operation performed last; it gives the outermost function. - Work from the outside inward to identify all three layers. - Apply the chain rule once for each layer of the composition. - Multiply the derivative factors in outer-to-inner order.

Solution

1. One valid decomposition is \(u(t)=e^t\), \(v(t)=\cos(t)\), and \(w(x)=2x+1\). 2. Their derivatives are \(u'(t)=e^t\), \(v'(t)=-\sin(t)\), and \(w'(x)=2\). 3. Applying the chain rule to the three-function composition gives \(f'(x)=u'(v(w(x)))v'(w(x))w'(x)\). 4. Substitute the functions and derivatives: \(f'(x)=e^{\cos(2x+1)}(-\sin(2x+1))\cdot 2\) \(=-2\sin(2x+1)e^{\cos(2x+1)}\).

Answer

a) One valid choice is \(u(t)=e^t\), \(v(t)=\cos(t)\), and \(w(x)=2x+1\). b) \(f'(x)=-2\sin(2x+1)e^{\cos(2x+1)}\)
52611012
Consider the family of functions \(g_{r,s}(x)=re^{2x}+se^x\), where \(r,s\in\mathbb{R}\). Find \(r\) and \(s\) so that the graph passes through \((0, 1)\) and has slope \(5\) there.

Hints

- Translate the point and slope information into two equations. - Use the chain rule for \(e^{2x}\). - Solve the resulting system of two linear equations.

Solution

1. The point condition gives \(g_{r,s}(0)=r+s=1\). 2. Differentiate using the chain rule: \(g_{r,s}'(x)=2re^{2x}+se^x\). 3. The slope condition gives \(g_{r,s}'(0)=2r+s=5\). 4. Subtract \(r+s=1\) from \(2r+s=5\) to obtain \(r=4\). 5. Substitute into \(r+s=1\): \(s=-3\).

Answer

\(r=4\) and \(s=-3\)
52611812
Consider the family of functions \(g_a(x)=2e^{ax}+1\), where \(a\in\mathbb{R}\setminus\{0\}\). a) Find \(g_a'(x)\). b) Find \(a\) so that the tangent line at \(x=0\) crosses the x-axis at \(x=-1\).

Hints

- Use the chain rule for \(e^{ax}\). - A point on the x-axis has y-coordinate \(0\). - Write the tangent line in terms of \(a\). - Substitute the given x-intercept into the tangent equation.

Solution

1. Apply the chain rule: \(g_a'(x)=2ae^{ax}\). 2. At \(x=0\), \(g_a(0)=3\) and \(g_a'(0)=2a\). 3. The tangent line is \(y=2ax+3\). 4. It must pass through \((-1, 0)\), so \(0=-2a+3\). 5. Therefore, \(a=\frac{3}{2}\).

Answer

a) \(g_a'(x)=2ae^{ax}\) b) \(a=\frac{3}{2}\)
52613812
Find the derivative of each function. a) \(f(x)=0.2e^{5-x^2}\) b) \(f(x)=e^{\frac{1}{2}x^2-x}\) c) \(f(x)=-\frac{3}{e^{4x+1}}\) d) \(f(x)=4e^{1-2x^3}\)

Hints

- Identify and differentiate the expression in each exponent. - Multiply the outer derivative by the inner derivative. - Rewrite a reciprocal exponential using a negative exponent. - Track negative signs carefully.

Solution

1. For \(f(x)=0.2e^{5-x^2}\), the inner derivative is \(-2x\). Thus, \(f'(x)=0.2\cdot(-2x)e^{5-x^2}=-0.4xe^{5-x^2}\). 2. For \(f(x)=e^{\frac{1}{2}x^2-x}\), the inner derivative is \(x-1\). Thus, \(f'(x)=(x-1)e^{\frac{1}{2}x^2-x}\). 3. Rewrite \(f(x)=-3e^{-4x-1}\). Then \(f'(x)=12e^{-4x-1}=\frac{12}{e^{4x+1}}\). 4. For \(f(x)=4e^{1-2x^3}\), the inner derivative is \(-6x^2\). Thus, \(f'(x)=-24x^2e^{1-2x^3}\).

Answer

a) \(f'(x)=-0.4xe^{5-x^2}\) b) \(f'(x)=(x-1)e^{\frac{1}{2}x^2-x}\) c) \(f'(x)=12e^{-4x-1}=\frac{12}{e^{4x+1}}\) d) \(f'(x)=-24x^2e^{1-2x^3}\)
52618812
Find the derivative of \(g(x)=\frac{1}{2}e^{\cos(2x)}\).

Hints

- Identify the nested functions in the exponent. - Apply the chain rule to \(e^{u(x)}\). - The exponent is itself a composition, so apply the chain rule again. - Recall the derivative of \(\cos(ax)\).

Solution

1. Let \(u(x)=\cos(2x)\). Applying the chain rule to the exponential function gives \(g'(x)=\frac{1}{2}e^{\cos(2x)}u'(x)\). 2. Apply the chain rule again to the cosine function: \(u'(x)=-\sin(2x)\cdot 2=-2\sin(2x)\). 3. Substitute and simplify: \(g'(x)=\frac{1}{2}e^{\cos(2x)}(-2\sin(2x))\) \(=-\sin(2x)e^{\cos(2x)}\).

Answer

\(g'(x)=-\sin(2x)e^{\cos(2x)}\)
52625312
Consider the family of functions \(f_{a,b}(x)=ae^{bx^2}\), where \(a,b\in\mathbb{R}\). Find \(a\) and \(b\) so that the graph passes through \((1, e^2)\) and has tangent slope \(4e^2\) there.

Hints

- Convert the point information into an equation. - Differentiate to convert the slope information into a second equation. - Two unknown parameters require two independent equations. - Substitute the repeated expression from one equation into the other.

Solution

1. The point condition gives \(ae^b=e^2\). 2. Apply the chain rule: \(f_{a,b}'(x)=2abxe^{bx^2}\). 3. The slope condition at \(x=1\) gives \(2abe^b=4e^2\). 4. Substitute \(ae^b=e^2\): \(2be^2=4e^2\), so \(b=2\). 5. Then \(ae^2=e^2\), so \(a=1\).

Answer

\(a=1\) and \(b=2\)
52645912
Find the derivative of each function. Simplify your results using the double-angle identity \(\sin(2\alpha)=2\sin(\alpha)\cos(\alpha)\). 1) \(f(x)=\sin^2(3x)\) 2) \(g(x)=\frac{3}{2}\cos^2(x)-\frac{3}{4}\cos(2x)\)

Hints

- View each squared trigonometric expression as a composition. - Apply the power rule before differentiating the trigonometric inner function. - Remember to differentiate the linear expressions \(3x\) and \(2x\). - Look for a product that matches the double-angle identity.

Solution

1. Write \(f(x)=(\sin(3x))^2\). Applying the chain rule twice gives \(f'(x)=2\sin(3x)\cos(3x)\cdot 3\). Since \(2\sin(3x)\cos(3x)=\sin(6x)\), \(f'(x)=3\sin(6x)\). 2. Differentiate each term of \(g\): \(g'(x)=\frac{3}{2}[2\cos(x)(-\sin(x))]-\frac{3}{4}[-\sin(2x)\cdot 2]\) \(=-3\sin(x)\cos(x)+\frac{3}{2}\sin(2x)\). Using \(2\sin(x)\cos(x)=\sin(2x)\), \(g'(x)=-\frac{3}{2}\sin(2x)+\frac{3}{2}\sin(2x)=0\).

Answer

1) \(f'(x)=3\sin(6x)\) 2) \(g'(x)=0\)
52651712
Find the derivative of each function. a) \(f(x)=e^{4x}-\frac{3}{e^x}\) b) \(f(x)=\sqrt{e^{6x}}\) c) \(f(x)=e^{kx^2}\), where \(k\in\mathbb{R}\)

Hints

- Rewrite reciprocal exponentials using negative exponents. - Simplify the square root before differentiating. - Use the chain rule for each exponential function. - Treat \(k\) as a constant.

Solution

1. Rewrite the first function as \(f(x)=e^{4x}-3e^{-x}\). Then \(f'(x)=4e^{4x}+3e^{-x}\). 2. Since \(e^{6x}>0\), \(\sqrt{e^{6x}}=e^{3x}\). Therefore, \(f'(x)=3e^{3x}\). 3. Treat \(k\) as a constant. The inner derivative of \(kx^2\) is \(2kx\), so \(f'(x)=2kxe^{kx^2}\).

Answer

a) \(f'(x)=4e^{4x}+3e^{-x}\) b) \(f'(x)=3e^{3x}\) c) \(f'(x)=2kxe^{kx^2}\)
52668312
Find the derivative of each function. a) \(f(x)=8e^{-0.5x}+2x^5\) b) \(g(x)=\frac{1}{5}e^{5x+2}-\sin(-4x)\) c) \(h(x)=(3x-4)e^{x^3}\)

Hints

- Decide which rule applies to each term. - Differentiate every exponent as part of the chain rule. - Use the product rule in part c. - Factor the common exponential factor when simplifying.

Solution

1. Differentiate each term in part a: \(f'(x)=8\cdot(-0.5)e^{-0.5x}+10x^4=-4e^{-0.5x}+10x^4\). 2. In part b, use the chain rule on both terms: \(g'(x)=e^{5x+2}+4\cos(4x)\). Here, \(\cos(-4x)=\cos(4x)\) because cosine is even. 3. In part c, use the product and chain rules: \(h'(x)=3e^{x^3}+(3x-4)(3x^2)e^{x^3}\) \(=(9x^3-12x^2+3)e^{x^3}\).

Answer

a) \(f'(x)=-4e^{-0.5x}+10x^4\) b) \(g'(x)=e^{5x+2}+4\cos(4x)\) c) \(h'(x)=(9x^3-12x^2+3)e^{x^3}\)
52748112
Find and simplify \(f'(x)\) for each function. a) \(f(x)=x^2e^{\sqrt{x}}\) b) \(f(x)=\frac{\sqrt{x}}{e^{x^2}}\) c) \(f(x)=\sqrt{e^{3x}+1}\)

Hints

- Identify the outer structure before choosing the product, quotient, or chain rule. - Rewrite radicals as rational powers when useful. - For the chain rule, multiply by the derivative of the inner function. - Simplify the original expression before differentiating when possible.

Solution

1. a) Apply the product rule and chain rule: \(f'(x)=2xe^{\sqrt{x}}+x^2e^{\sqrt{x}}\frac{1}{2\sqrt{x}}=xe^{\sqrt{x}}\left(2+\frac{1}{2}\sqrt{x}\right)\). 2. b) Apply the quotient rule and chain rule: \(f'(x)=\frac{\frac{1}{2\sqrt{x}}e^{x^2}-\sqrt{x}e^{x^2}(2x)}{e^{2x^2}}=\frac{1-4x^2}{2\sqrt{x}e^{x^2}}\). 3. c) Apply the chain rule: \(f'(x)=\frac{1}{2\sqrt{e^{3x}+1}}\cdot3e^{3x}=\frac{3e^{3x}}{2\sqrt{e^{3x}+1}}\).

Answer

a) \(f'(x)=xe^{\sqrt{x}}\left(2+\frac{1}{2}\sqrt{x}\right)\) b) \(f'(x)=\frac{1-4x^2}{2\sqrt{x}e^{x^2}}\) c) \(f'(x)=\frac{3e^{3x}}{2\sqrt{e^{3x}+1}}\)
52748212
For \(x>0\), let \(f(x)=e^{\sqrt{x}}\) and \(g(x)=\sqrt{e^x}\). Find both derivatives. Then determine which graph has the greater slope at \(x=1\).

Hints

- The derivative at a point gives the graph's slope there. - Rewrite \(\sqrt{e^x}\) as a single exponential expression before differentiating. - “Greater slope” means the larger derivative value. - Evaluate both derivatives at \(x=1\) and compare.

Solution

1. By the chain rule, \(f'(x)=e^{\sqrt{x}}\frac{1}{2\sqrt{x}}=\frac{e^{\sqrt{x}}}{2\sqrt{x}}\). 2. Since \(g(x)=e^{x/2}\), \(g'(x)=\frac{1}{2}e^{x/2}\). 3. At \(x=1\), \(f'(1)=\frac{e}{2}\) and \(g'(1)=\frac{\sqrt{e}}{2}\). Because \(e>\sqrt{e}\), \(f'(1)>g'(1)\).

Answer

\(f'(x)=\frac{e^{\sqrt{x}}}{2\sqrt{x}}\) and \(g'(x)=\frac{1}{2}e^{x/2}\). The graph of \(f\) has the greater slope at \(x=1\).
52748312
Let \(f(x)=\ln(x)\) and \(g(x)=2x^2+5\). 1) Write a formula for the composition \(h(x)=f(g(x))\), and find \(h'(x)\). 2) Now consider the reverse composition \(k(x)=g(f(x))\). Write a formula for \(k(x)\), find \(k'(x)\), and show that it can be written as \(k'(x)=\frac{4\ln(x)}{x}\).

Hints

- Identify which function is the inner function in each composition. - Use the chain rule for a function of the form \(u(v(x))\). - Recall the derivative rules for logarithmic and power functions. - In part 2, the square applies to the entire logarithmic expression.

Solution

1. The first composition is \(h(x)=\ln(2x^2+5)\). By the chain rule, \(h'(x)=\frac{1}{2x^2+5}(4x)=\frac{4x}{2x^2+5}\). Since \(2x^2+5>0\) for every real \(x\), the domain of \(h\) is all real numbers. 2. The reverse composition is \(k(x)=2(\ln(x))^2+5\), which is defined for \(x>0\). Applying the chain rule gives \(k'(x)=4\ln(x)\left(\frac{1}{x}\right)=\frac{4\ln(x)}{x}\).

Answer

1) \(h(x)=\ln(2x^2+5)\), \(h'(x)=\frac{4x}{2x^2+5}\), and the domain of \(h\) is \((-\infty, \infty)\). 2) \(k(x)=2(\ln(x))^2+5\), \(k'(x)=\frac{4\ln(x)}{x}\), and the domain of \(k\) is \((0, \infty)\).
52748412
Consider \(p(x)=(x^3-4)^{-2}\). 1) Identify an outer function \(u\) and an inner function \(v\) such that \(p(x)=u(v(x))\). 2) Use the chain rule to find \(p'(x)\). 3) Find the x-coordinate of the point where the graph of \(p\) has a horizontal tangent.

Hints

- Rewrite the expression as an outer power applied to an inner polynomial. - A horizontal tangent occurs where the derivative is zero. - Apply the power rule and then multiply by the derivative of the inner function. - A fraction equals zero when its numerator is zero and its denominator is nonzero.

Solution

1. One possible decomposition is \(u(t)=t^{-2}\) and \(v(x)=x^3-4\). 2. Since \(u'(t)=-2t^{-3}\) and \(v'(x)=3x^2\), the chain rule gives \(p'(x)=-2(x^3-4)^{-3}(3x^2)\) \(=-\frac{6x^2}{(x^3-4)^3}\). 3. A horizontal tangent occurs where \(p'(x)=0\). A rational expression is zero when its numerator is zero and its denominator is nonzero. Thus, \(-6x^2=0\), so \(x=0\). At \(x=0\), the denominator is nonzero, so this value is in the domain.

Answer

1) One possible choice is \(u(t)=t^{-2}\) and \(v(x)=x^3-4\). 2) \(p'(x)=-\frac{6x^2}{(x^3-4)^3}\) 3) \(x=0\)
52748612
Let \(f(x)=\sqrt[3]{\sin(2x)+2}\). Find \(f'(x)\).

Hints

- Rewrite the cube root as a rational power. - Identify the outer, middle, and inner functions. - Remember the derivative of \(\sin(2x)\), including the derivative of its argument. - A negative rational exponent can be rewritten as a radical in the denominator.

Solution

1. Rewrite the function as \(f(x)=(\sin(2x)+2)^{\frac{1}{3}}\). 2. Apply the chain rule to the outer power and then to \(\sin(2x)\): \(f'(x)=\frac{1}{3}(\sin(2x)+2)^{-\frac{2}{3}}\cdot2\cos(2x)\). 3. Rewrite with a radical: \(f'(x)=\frac{2\cos(2x)}{3\sqrt[3]{(\sin(2x)+2)^2}}\).

Answer

\(f'(x)=\frac{2\cos(2x)}{3\sqrt[3]{(\sin(2x)+2)^2}}\)
52749712
The graph of \(f(x)=a\sqrt{x+b}+c\) is obtained from \(g(x)=\sqrt{x}\) by a vertical stretch by a factor of \(3\), a shift \(4\) units left, and a shift \(2\) units down. 1. Write the formula for \(f\). 2. Find the equation of the tangent line to the graph of \(f\) at \(x=5\).

Hints

- Match each graph transformation to its parameter in the function formula. - A shift left changes the expression inside the radical to \(x+4\). - Differentiate the square-root function with the chain rule. - The derivative at \(x=5\) gives the tangent slope.

Solution

1. The transformations give \(a=3\), \(b=4\), and \(c=-2\), so \(f(x)=3\sqrt{x+4}-2\). 2. Differentiate: \(f'(x)=\frac{3}{2\sqrt{x+4}}\). 3. At \(x=5\), the slope is \(f'(5)=\frac{3}{2\sqrt{9}}=\frac{1}{2}\), and the point is \((5,7)\). 4. Using point-slope form, \(y-7=\frac{1}{2}(x-5)\), so \(y=\frac{1}{2}x+\frac{9}{2}\).

Answer

1. \(f(x)=3\sqrt{x+4}-2\) 2. \(y=\frac{1}{2}x+\frac{9}{2}\)
52749812
Let \(f(x)=\sqrt{4x+12}\). 1. First factor the expression under the radical. Then describe how the graph of \(f\) is obtained from the graph of \(g(x)=\sqrt{x}\). 2. Find the value \(x_0\) at which the slope of the graph of \(f\) is exactly \(1\).

Hints

- Use radical properties to factor the expression before describing the transformations. - A factor outside the radical creates a vertical stretch. - The derivative gives the graph's slope. - Set the derivative equal to the target slope and solve.

Solution

1. Rewrite \(f(x)=\sqrt{4(x+3)}=2\sqrt{x+3}\). The graph is vertically stretched by a factor of \(2\) and shifted \(3\) units left. 2. Differentiate: \(f'(x)=\frac{1}{\sqrt{x+3}}\). 3. Set the derivative equal to \(1\): \(\frac{1}{\sqrt{x+3}}=1\). Thus, \(x+3=1\), so \(x_0=-2\).

Answer

1. \(f(x)=2\sqrt{x+3}\); vertical stretch by \(2\) and shift \(3\) units left 2. \(x_0=-2\)
52750512
Let \(f(x)=\sqrt{x+4}\) and \(g(x)=4-\sqrt{x}\). a) Find the largest real domains \(D_f\) and \(D_g\). b) Find the intersection point \(S\) of the graphs of \(f\) and \(g\). c) Find the equation of the tangent line to the graph of \(f\) at \(S\).

Hints

- Require each square-root radicand to be nonnegative. - Set the function values equal to find an intersection. - After squaring, check the resulting solution in the original equation. - The derivative at the intersection gives the tangent slope. - Use point-slope form for the tangent line.

Solution

1. The radicands must be nonnegative, so \(D_f=[-4,\infty)\) and \(D_g=[0,\infty)\). 2. Set the functions equal: \(\sqrt{x+4}=4-\sqrt{x}\). Squaring and simplifying gives \(8\sqrt{x}=12\), so \(\sqrt{x}=\frac{3}{2}\) and \(x=\frac{9}{4}\). Then \(y=\frac{5}{2}\), so \(S=\left(\frac{9}{4},\frac{5}{2}\right)\). 3. Since \(f'(x)=\frac{1}{2\sqrt{x+4}}\), the tangent slope is \(f'\left(\frac{9}{4}\right)=\frac{1}{5}\). 4. Using point-slope form, \(y-\frac{5}{2}=\frac{1}{5}\left(x-\frac{9}{4}\right)\), so \(y=\frac{1}{5}x+\frac{41}{20}\).

Answer

a) \(D_f=[-4,\infty)\); \(D_g=[0,\infty)\) b) \(S=\left(\frac{9}{4},\frac{5}{2}\right)\) c) \(y=\frac{1}{5}x+\frac{41}{20}\)
52750612
Let \(f(x)=\sqrt{2x}\) and \(g(x)=\sqrt{6-x}\). a) Find the intercepts of both graphs with the coordinate axes. b) Show algebraically that \(S=(2,2)\) is the only point shared by the two graphs. c) Use derivatives to determine whether the tangent lines to the graphs at \(S\) are perpendicular.

Hints

- Set \(y=0\) for x-intercepts and \(x=0\) for y-intercepts. - Set the two function expressions equal to find shared points. - Apply the chain rule to each square-root function. - Two nonvertical lines are perpendicular when the product of their slopes is \(-1\).

Solution

1. a) For \(f\), \(f(0)=0\), so the only axis intercept is \((0,0)\). For \(g\), \(g(0)=\sqrt{6}\), giving \((0,\sqrt{6})\), and \(g(6)=0\), giving \((6,0)\). 2. b) Set the functions equal: \(\sqrt{2x}=\sqrt{6-x}\). Squaring gives \(2x=6-x\), so \(x=2\) and \(y=2\). The resulting linear equation has only one solution, and it checks in the original equation. 3. c) The derivatives are \(f'(x)=\frac{1}{\sqrt{2x}}\) and \(g'(x)=-\frac{1}{2\sqrt{6-x}}\). 4. At \(x=2\), the slopes are \(m_f=\frac{1}{2}\) and \(m_g=-\frac{1}{4}\). Their product is \(-\frac{1}{8}\ne-1\), so the tangent lines are not perpendicular.

Answer

a) For \(f\): \((0,0)\); for \(g\): \((0,\sqrt{6})\) and \((6,0)\) b) The only shared point is \((2,2)\). c) No. The tangent slopes have product \(-\frac{1}{8}\), not \(-1\).
52750712
Let \(f(x)=\sqrt{6-3x}+2\), with its largest real domain \(D_f\). a) Find \(D_f\). b) Find the equation of the tangent line \(t\) to the graph of \(f\) at \(x_0=-1\). c) Find the coordinates of the y-intercept of \(t\).

Hints

- A square-root radicand must be nonnegative. - A tangent line requires both the point on the graph and the derivative there. - Use the chain rule to differentiate the square root. - A point on the y-axis has \(x=0\).

Solution

1. a) Require \(6-3x\ge0\), which gives \(x\le2\). Thus, \(D_f=(-\infty,2]\). 2. b) The point of tangency is \((-1,f(-1))=(-1,5)\). 3. Differentiate: \(f'(x)=-\frac{3}{2\sqrt{6-3x}}\), defined for \(x<2\). Therefore, \(f'(-1)=-\frac{1}{2}\). 4. Using point-slope form, \(y-5=-\frac{1}{2}(x+1)\), so \(t\) is \(y=-\frac{1}{2}x+\frac{9}{2}\). 5. c) Set \(x=0\). The y-intercept is \(\left(0,\frac{9}{2}\right)\).

Answer

a) \(D_f=(-\infty,2]\) b) \(t:y=-\frac{1}{2}x+\frac{9}{2}\) c) \(\left(0,\frac{9}{2}\right)\)
52750812
Let \(k(x)=4-\sqrt{2x+1}\), with its largest real domain \(D_k\). a) Find \(D_k\). b) Find the value \(x_0\) at which the tangent line to the graph of \(k\) has slope \(-\frac{1}{5}\). c) Find the equation of that tangent line.

Hints

- Require the expression under the square root to be nonnegative. - Set the derivative equal to the specified tangent slope. - To solve a reciprocal square-root equation, isolate the radical before squaring. - A line is determined by a slope and one point.

Solution

1. a) Require \(2x+1\ge0\), so \(D_k=\left[-\frac{1}{2},\infty\right)\). 2. Differentiate: \(k'(x)=-\frac{1}{\sqrt{2x+1}}\). 3. Set \(k'(x_0)=-\frac{1}{5}\): \(\sqrt{2x_0+1}=5\), so \(2x_0+1=25\) and \(x_0=12\). 4. The point of tangency is \((12,k(12))=(12,-1)\). 5. Using point-slope form, \(y+1=-\frac{1}{5}(x-12)\), so \(y=-\frac{1}{5}x+\frac{7}{5}\).

Answer

a) \(D_k=\left[-\frac{1}{2},\infty\right)\) b) \(x_0=12\) c) \(y=-\frac{1}{5}x+\frac{7}{5}\)
52750912
Let \(f(x)=\sqrt{12-3x^2}\) be real-valued. a) Find the largest possible domain \(D_f\). b) Find \(f'(x)\). c) Find the equation of the tangent line to the graph of \(f\) at \(x=1\).

Hints

- A square-root radicand must be nonnegative. - Apply the chain rule to the square-root function. - A tangent line needs the function value and derivative value at the given input. - Use point-slope form after finding the slope.

Solution

1. a) Require \(12-3x^2\ge0\), or \(x^2\le4\). Therefore, \(D_f=[-2,2]\). 2. b) By the chain rule, \(f'(x)=\frac{-6x}{2\sqrt{12-3x^2}}=-\frac{3x}{\sqrt{12-3x^2}}\). 3. c) At \(x=1\), \(f(1)=3\) and \(f'(1)=-1\). 4. Using point-slope form, \(y-3=-(x-1)\), so \(y=-x+4\).

Answer

a) \(D_f=[-2,2]\) b) \(f'(x)=-\frac{3x}{\sqrt{12-3x^2}}\) c) \(y=-x+4\)
52751212
Let \(h(x)=3-2\sqrt{x+1}\), with its largest real domain \(D_h\). a) Find \(D_h\), and describe step by step how the graph of \(h\) is obtained from \(w(x)=\sqrt{x}\). b) Find the x-intercept of the graph of \(h\). c) Find the value \(x_0\) at which the tangent line has slope \(-\frac{1}{2}\).

Hints

- Identify which operations occur inside and outside the radical. - Find an x-intercept by setting the function equal to \(0\). - Isolate the radical before squaring. - Differentiate the square-root function to obtain its slope function. - Set the derivative equal to the specified slope.

Solution

1. a) Require \(x+1\ge0\), so \(D_h=[-1,\infty)\). Starting with \(w(x)=\sqrt{x}\), shift \(1\) unit left, vertically stretch by \(2\), reflect across the x-axis, and shift \(3\) units up. 2. b) Set \(h(x)=0\): \(3-2\sqrt{x+1}=0\), so \(\sqrt{x+1}=\frac{3}{2}\). Then \(x+1=\frac{9}{4}\), giving \(x=\frac{5}{4}\). The intercept is \(\left(\frac{5}{4},0\right)\). 3. c) Differentiate: \(h'(x)=-\frac{1}{\sqrt{x+1}}\). Set \(h'(x_0)=-\frac{1}{2}\), so \(\sqrt{x_0+1}=2\), and \(x_0=3\).

Answer

a) \(D_h=[-1,\infty)\); shift left \(1\), vertically stretch by \(2\), reflect across the x-axis, and shift up \(3\) b) \(\left(\frac{5}{4},0\right)\) c) \(x_0=3\)
52751312
Let \(f(x)=\frac{1}{2}\sqrt{x+4}-3\). a) Describe how the graph of \(f\) is obtained from \(g(x)=\sqrt{x}\). b) Find \(f'(x)\). c) Find the point \(P\) on the graph of \(f\) where the tangent line is parallel to \(y=\frac{1}{8}x+5\).

Hints

- Match each parameter to a horizontal shift, vertical scale, or vertical shift. - Rewrite the square root as a rational power before differentiating if helpful. - Parallel lines have equal slopes. - Substitute the x-coordinate into \(f\) to find the point's y-coordinate.

Solution

1. a) Shift the square-root graph \(4\) units left, vertically shrink it by a factor of \(\frac{1}{2}\), and shift it \(3\) units down. 2. b) By the chain rule, \(f'(x)=\frac{1}{4\sqrt{x+4}}\). 3. c) Parallel lines have equal slopes, so set \(f'(x)=\frac{1}{8}\). Then \(\frac{1}{4\sqrt{x+4}}=\frac{1}{8}\), so \(\sqrt{x+4}=2\), giving \(x=0\). 4. Since \(f(0)=\frac{1}{2}\sqrt{4}-3=-2\), the point is \(P=(0,-2)\).

Answer

a) Shift left \(4\), vertically shrink by \(\frac{1}{2}\), and shift down \(3\) b) \(f'(x)=\frac{1}{4\sqrt{x+4}}\) c) \(P=(0,-2)\)
52751612
Let \(g(x)=\sqrt{x^4+2x^2+5}\). a) Show algebraically that the graph of \(g\) is symmetric about the y-axis. b) Find \(g'(x)\), and use the symmetry of \(g\) to explain why \(g'(0)=0\).

Hints

- Even powers do not change when \(x\) is replaced by \(-x\). - Use the chain rule for the square-root function. - A smooth graph symmetric about the y-axis has a horizontal tangent where it crosses that axis. - Determine the parity of the derivative of an even function.

Solution

1. a) \(g(-x)=\sqrt{(-x)^4+2(-x)^2+5}=\sqrt{x^4+2x^2+5}=g(x)\). Thus, \(g\) is even, so its graph is symmetric about the y-axis. 2. b) By the chain rule, \(g'(x)=\frac{4x^3+4x}{2\sqrt{x^4+2x^2+5}}=\frac{2x^3+2x}{\sqrt{x^4+2x^2+5}}\). 3. The derivative of an even differentiable function is odd. Therefore, \(g'(-x)=-g'(x)\), and at \(x=0\), \(g'(0)=-g'(0)\), which implies \(g'(0)=0\).

Answer

a) Since \(g(-x)=g(x)\), the graph is symmetric about the y-axis. b) \(g'(x)=\frac{2x^3+2x}{\sqrt{x^4+2x^2+5}}\), and \(g'(0)=0\) because the derivative of an even differentiable function is odd.
52752112
Let \(f(x)=\sqrt{12-x}\) and \(g(x)=\sqrt{x+4}\), with largest real domains \(D_f\) and \(D_g\). a) Find \(D_f\) and \(D_g\), and find the x-intercept of each graph. b) Find the intersection point \(S\) of the two graphs. c) Find the equations of the tangent lines to both graphs at \(S\).

Hints

- A square-root radicand must be nonnegative. - Set a function equal to \(0\) to find an x-intercept. - Set the two functions equal to find a shared point. - Use each derivative to find the corresponding tangent slope. - Write each tangent line in point-slope form.

Solution

1. a) Require each radicand to be nonnegative. Thus, \(D_f=(-\infty,12]\) and \(D_g=[-4,\infty)\). The x-intercepts are \((12,0)\) and \((-4,0)\), respectively. 2. b) Set the functions equal: \(12-x=x+4\), so \(x=4\). Then \(y=\sqrt{8}=2\sqrt{2}\), giving \(S=(4,2\sqrt{2})\). 3. c) The derivatives are \(f'(x)=-\frac{1}{2\sqrt{12-x}}\) and \(g'(x)=\frac{1}{2\sqrt{x+4}}\). 4. At \(x=4\), the slopes are \(-\frac{\sqrt{2}}{8}\) and \(\frac{\sqrt{2}}{8}\). 5. Using point-slope form, the tangent lines are \(t_f:y=-\frac{\sqrt{2}}{8}x+\frac{5\sqrt{2}}{2}\) and \(t_g:y=\frac{\sqrt{2}}{8}x+\frac{3\sqrt{2}}{2}\).

Answer

a) \(D_f=(-\infty,12]\), with x-intercept \((12,0)\); \(D_g=[-4,\infty)\), with x-intercept \((-4,0)\) b) \(S=(4,2\sqrt{2})\) c) \(t_f:y=-\frac{\sqrt{2}}{8}x+\frac{5\sqrt{2}}{2}\); \(t_g:y=\frac{\sqrt{2}}{8}x+\frac{3\sqrt{2}}{2}\)
52752312
Let \(f(x)=2\sqrt{7-x}+x\), with largest real domain \(D\). a) Find \(D\). b) Find the equation of the tangent line to the graph of \(f\) at \(x=3\).

Hints

- Require the square-root radicand to be nonnegative. - Find the graph point at the given x-coordinate. - Apply the chain rule to the radical term. - A line is determined by one point and its slope.

Solution

1. a) Require \(7-x\ge0\), so \(D=(-\infty,7]\). 2. At \(x=3\), \(f(3)=2\sqrt{4}+3=7\). 3. By the chain rule, \(f'(x)=1-\frac{1}{\sqrt{7-x}}\), so \(f'(3)=\frac{1}{2}\). 4. Using point-slope form, \(y-7=\frac{1}{2}(x-3)\), so \(y=\frac{1}{2}x+\frac{11}{2}\).

Answer

a) \(D=(-\infty,7]\) b) \(y=\frac{1}{2}x+\frac{11}{2}\)
52752412
Let \(g(x)=3\sqrt{2x+2}-x\), with its largest real domain. a) Find the domain of \(g\). b) A point \(P\) on the graph has a tangent line with slope \(\frac{1}{2}\). Find the coordinates of \(P\).

Hints

- Require the expression under the radical to be nonnegative. - A tangent slope is a value of the derivative. - Set the derivative equal to the specified slope and solve. - Substitute the resulting x-coordinate into the original function.

Solution

1. a) Require \(2x+2\ge0\), so the domain is \([-1,\infty)\). 2. Differentiate: \(g'(x)=\frac{3}{\sqrt{2x+2}}-1\). 3. Set the derivative equal to \(\frac{1}{2}\): \(\frac{3}{\sqrt{2x+2}}-1=\frac{1}{2}\). Then \(\sqrt{2x+2}=2\), so \(x=1\). 4. Evaluate \(g(1)=3\sqrt{4}-1=5\). Thus, \(P=(1,5)\).

Answer

a) \([-1,\infty)\) b) \(P=(1,5)\)
52752612
Let \(g(x)=4-2\sqrt{x+1}\), with largest real domain \(D_g\). a) Find the intercepts of the graph of \(g\) with the coordinate axes. b) Show algebraically that the tangent line to the graph of \(g\) at its y-intercept has an inclination angle of \(135^\circ\), measured counterclockwise from the positive x-axis. c) Describe step by step how the graph of \(g\) is obtained from \(w(x)=\sqrt{x}\).

Hints

- Set \(x=0\) for the y-intercept and \(y=0\) for the x-intercept. - The derivative gives the tangent slope. - Relate the slope to the tangent of the inclination angle. - Read transformations from the operations inside and outside the square root.

Solution

1. a) The y-intercept is \((0,g(0))=(0,2)\). For the x-intercept, solve \(4-2\sqrt{x+1}=0\), giving \(x=3\). Thus, the x-intercept is \((3,0)\). 2. b) Differentiate: \(g'(x)=-\frac{1}{\sqrt{x+1}}\). At \(x=0\), the tangent slope is \(-1\). Since \(\tan(135^\circ)=-1\), the inclination angle is \(135^\circ\). 3. c) Starting with \(w(x)=\sqrt{x}\), shift \(1\) unit left, vertically stretch by \(2\), reflect across the x-axis, and shift \(4\) units up.

Answer

a) y-intercept \((0,2)\); x-intercept \((3,0)\) b) \(g'(0)=-1=\tan(135^\circ)\), so the inclination angle is \(135^\circ\). c) Shift left \(1\), vertically stretch by \(2\), reflect across the x-axis, and shift up \(4\).
52753612
Let \(g(x)=\sqrt{2x}\) for \(x>0\). a) Show that the normal line to the graph of \(g\) at \(B=(x_0,g(x_0))\) always intersects the x-axis at a point \(S=(x_n,0)\) whose x-coordinate is exactly \(1\) greater than \(x_0\). b) For \(x_0=4\), use the result from part a to find \(S\) and the distance from the origin \(O=(0,0)\) to \(S\).

Hints

- The normal slope is the negative reciprocal of the tangent slope. - Set the normal line equal to \(0\) to find its x-intercept. - Compare the resulting x-coordinate with \(x_0\). - A point on the x-axis is as far from the origin as the absolute value of its x-coordinate.

Solution

1. Differentiate: \(g'(x)=\frac{1}{\sqrt{2x}}\). 2. The normal slope at \(x_0\) is \(m_n=-\sqrt{2x_0}\). 3. The normal equation is \(y=-\sqrt{2x_0}(x-x_0)+\sqrt{2x_0}\). 4. a) Set \(y=0\): \(0=-\sqrt{2x_0}(x_n-x_0)+\sqrt{2x_0}\). Since \(x_0>0\), divide by \(\sqrt{2x_0}\) to obtain \(x_n=x_0+1\). 5. b) For \(x_0=4\), \(x_n=5\), so \(S=(5,0)\). The distance \(OS\) is \(5\) units.

Answer

a) \(x_n=x_0+1\) b) \(S=(5,0)\), and \(OS=5\) units
52754412
Let \(h(x)=3\sqrt{4-x}\). Find the equation of the normal line to the graph of \(h\) at its y-intercept. Also find the inclination angle of the tangent line at that point, measured counterclockwise from the positive x-axis.

Hints

- A y-intercept has x-coordinate \(0\). - The tangent slope is the derivative value at the point. - Relate a line's slope to the tangent of its inclination angle. - The normal slope is the negative reciprocal of the tangent slope.

Solution

1. The y-intercept is \(P=(0,h(0))=(0,6)\). 2. By the chain rule, \(h'(x)=-\frac{3}{2\sqrt{4-x}}\), so the tangent slope at \(x=0\) is \(m_t=-\frac{3}{4}\). 3. The inclination angle \(\alpha\) satisfies \(\tan(\alpha)=-\frac{3}{4}\) with \(0^\circ<\alpha<180^\circ\). Thus, \(\alpha\approx143.13^\circ\). 4. The normal slope is \(m_n=-\frac{1}{m_t}=\frac{4}{3}\). Through \((0,6)\), the normal line is \(y=\frac{4}{3}x+6\).

Answer

Normal line: \(y=\frac{4}{3}x+6\) Tangent inclination angle: \(\alpha\approx143.13^\circ\)
52754512
Consider the family of functions \(f_a(x)=\sqrt{2ax-a^2}\), where \(a>0\). a) Find the maximal domain in terms of \(a\). b) Find \(f_a'(x)\). c) Find \(a\) so that the slope at \(x=2\) is \(0.5\).

Hints

- The radicand must be nonnegative. - Use the chain rule for the square root. - The derivative value gives the slope. - Isolate and square a radical equation only after checking signs.

Solution

1. Require \(2ax-a^2\geq0\). Since \(a>0\), this is equivalent to \(x\geq\frac{a}{2}\). Thus, the domain is \(\left[\frac{a}{2},\infty\right)\). 2. Apply the chain rule: \(f_a'(x)=\frac{a}{\sqrt{2ax-a^2}}\). 3. Set \(f_a'(2)=\frac{1}{2}\): \(\frac{a}{\sqrt{4a-a^2}}=\frac{1}{2}\). 4. Squaring gives \(a^2=\frac{1}{4}(4a-a^2)\), so \(5a^2-4a=0\). 5. Since \(a>0\), \(a=\frac{4}{5}\). The value \(x=2\) lies in the corresponding domain, so the solution is valid.

Answer

a) Domain: \(\left[\frac{a}{2},\infty\right)\) b) \(f_a'(x)=\frac{a}{\sqrt{2ax-a^2}}\) c) \(a=\frac{4}{5}\)
52755112
Let \(f(x)=\sqrt{x^2-6x+5}\). Find the largest real domain \(D_f\), and find \(f'(x)\).

Hints

- Require the square-root radicand to be nonnegative. - Use the zeros of the quadratic to make a sign chart. - Apply the chain rule to the composite function. - Simplify the factor of \(2\) after differentiating.

Solution

1. Require \(x^2-6x+5\ge0\). Since \(x^2-6x+5=(x-1)(x-5)\), the expression is nonnegative for \(x\le1\) or \(x\ge5\). 2. Therefore, \(D_f=(-\infty,1]\cup[5,\infty)\). 3. By the chain rule, \(f'(x)=\frac{2x-6}{2\sqrt{x^2-6x+5}}=\frac{x-3}{\sqrt{x^2-6x+5}}\), for \(x<1\) or \(x>5\).

Answer

\(D_f=(-\infty,1]\cup[5,\infty)\); \(f'(x)=\frac{x-3}{\sqrt{x^2-6x+5}}\) on the interior of \(D_f\)
52756912
Let \(f(x)=3-2\sqrt{x+4}\) for \(x\ge-4\). 1. Describe how the graph of \(f\) is obtained from \(g(x)=\sqrt{x}\). 2. Find \(f'(x)\) and the slope of the graph at \(x=0\). 3. Find the range of \(f\).

Hints

- Read horizontal changes from inside the radical and vertical changes from outside it. - Apply the chain rule to differentiate. - Substitute the given input into the derivative to find the slope. - Use the endpoint value and long-run behavior to determine the range.

Solution

1. Shift the square-root graph \(4\) units left, vertically stretch it by \(2\), reflect it across the x-axis, and shift it \(3\) units up. 2. By the chain rule, \(f'(x)=-\frac{1}{\sqrt{x+4}}\), for \(x>-4\). Thus, \(f'(0)=-\frac{1}{2}\). 3. At the left endpoint, \(f(-4)=3\), which is the greatest value. As \(x\to\infty\), \(f(x)\to-\infty\). Therefore, the range is \((-\infty,3]\).

Answer

1. Shift left \(4\), vertically stretch by \(2\), reflect across the x-axis, and shift up \(3\). 2. \(f'(x)=-\frac{1}{\sqrt{x+4}}\); \(f'(0)=-\frac{1}{2}\) 3. \((-\infty,3]\)
52757712
Let \(f(x)=\sqrt{100-x^2}\). Find the equation of the tangent line to the graph of \(f\) that is parallel to \(y=\frac{3}{4}x+10\).

Hints

- Parallel lines have equal slopes. - Set the derivative equal to the target slope. - Apply the chain rule to the square-root function. - Check solutions after squaring because signs may have been lost. - Use point-slope form once the point of tangency is known.

Solution

1. Differentiate: \(f'(x)=-\frac{x}{\sqrt{100-x^2}}\). 2. A parallel tangent must have slope \(\frac{3}{4}\), so solve \(-\frac{x}{\sqrt{100-x^2}}=\frac{3}{4}\). 3. Squaring gives \(16x^2=9(100-x^2)\), so \(x^2=36\). Checking the original equation shows that the positive slope requires \(x=-6\). 4. The point of tangency is \((-6,f(-6))=(-6,8)\). 5. Using point-slope form, \(y-8=\frac{3}{4}(x+6)\), so \(y=\frac{3}{4}x+\frac{25}{2}\).

Answer

\(y=\frac{3}{4}x+\frac{25}{2}\)
52757812
Let \(g(x)=\sqrt{x^2+12}\). Find the equation of the tangent line to the graph of \(g\) that is perpendicular to \(y=-2x+1\).

Hints

- Perpendicular nonvertical lines have slopes whose product is \(-1\). - Set the derivative equal to the required tangent slope. - Check the sign after squaring. - Use the point and slope to write the line equation.

Solution

1. Differentiate: \(g'(x)=\frac{x}{\sqrt{x^2+12}}\). 2. A line perpendicular to a line of slope \(-2\) has slope \(\frac{1}{2}\). 3. Solve \(\frac{x}{\sqrt{x^2+12}}=\frac{1}{2}\). Squaring gives \(4x^2=x^2+12\), so \(x^2=4\). Checking the original equation gives \(x=2\). 4. The point of tangency is \((2,g(2))=(2,4)\). 5. Using point-slope form, \(y-4=\frac{1}{2}(x-2)\), so \(y=\frac{1}{2}x+3\).

Answer

\(y=\frac{1}{2}x+3\)
52758112
Let \(f(x)=2\sqrt{25-x^2}\) on its largest real domain \(D\). a) Find \(D\). b) Use the chain rule to show that \(f'(x)=-\frac{2x}{\sqrt{25-x^2}}\). c) Find the slope of the tangent line at \(x=3\).

Hints

- A square-root radicand must be nonnegative. - Apply the chain rule: outer derivative times inner derivative. - The tangent slope at a point is the derivative value there.

Solution

1. a) Require \(25-x^2\ge0\), so \(D=[-5,5]\). 2. b) Apply the chain rule: \(f'(x)=2\cdot\frac{1}{2\sqrt{25-x^2}}(-2x)=-\frac{2x}{\sqrt{25-x^2}}\), for \(-5<x<5\). 3. c) \(f'(3)=-\frac{6}{\sqrt{16}}=-\frac{3}{2}\).

Answer

a) \(D=[-5,5]\) b) \(f'(x)=-\frac{2x}{\sqrt{25-x^2}}\) for \(-5<x<5\) c) \(-\frac{3}{2}\)
52758212
Let \(g(x)=\sqrt{2x^2+17}\). a) Find \(g'(x)\). b) Find the equation of the tangent line to the graph of \(g\) at \(x_0=2\).

Hints

- Apply the chain rule and multiply by the derivative of the radicand. - A tangent line requires the graph point and derivative value. - Use point-slope form to write the line.

Solution

1. a) By the chain rule, \(g'(x)=\frac{4x}{2\sqrt{2x^2+17}}=\frac{2x}{\sqrt{2x^2+17}}\). 2. b) At \(x=2\), \(g(2)=5\) and \(g'(2)=\frac{4}{5}\). 3. Using point-slope form, \(y-5=\frac{4}{5}(x-2)\), so \(y=\frac{4}{5}x+\frac{17}{5}\).

Answer

a) \(g'(x)=\frac{2x}{\sqrt{2x^2+17}}\) b) \(y=\frac{4}{5}x+\frac{17}{5}\)
52758812
Let \(g(x)=\ln(12-4x)\). a) Find the maximal domain of \(g\). b) Find \(g'(x)\) using the chain rule. c) Find the slope of the graph at \(x=2\).

Hints

- Require the logarithm’s input to be positive. - Differentiate the outer logarithm and multiply by the inner derivative. - Substitute \(x=2\) into the derivative.

Solution

1. The logarithm requires \(12-4x>0\). Solving gives \(x<3\), so \(D_g=(-\infty, 3)\). 2. Apply the chain rule: \(g'(x)=\frac{-4}{12-4x}=\frac{1}{x-3}\). 3. Evaluate the derivative at \(x=2\): \(g'(2)=\frac{1}{2-3}=-1\).

Answer

a) \(D_g=(-\infty, 3)\) b) \(g'(x)=\frac{1}{x-3}\) c) The slope is \(-1\).
52761312
Let \(f(x)=\ln(x^4)\) on its maximal domain. a) Find the domain. b) Find \(f'(x)\) using the chain rule. c) A student claims, “Because \(\ln(x^4)=4\ln x\), we can immediately write \(f'(x)=\frac{4}{x}\) for every \(x\) in the domain.” Evaluate the student’s reasoning, paying close attention to domains.

Hints

- Determine when the logarithm’s argument is positive. - Apply the chain rule as outer derivative times inner derivative. - Compare the domains of \(\ln(x^4)\) and \(\ln x\). - Consider how absolute value produces a valid identity for negative inputs.

Solution

1. The logarithm requires \(x^4>0\), which holds exactly when \(x\ne0\). Therefore, \(D_f=\mathbb{R}\setminus\{0\}\). 2. Apply the chain rule: \(f'(x)=\frac{1}{x^4}(4x^3)=\frac{4}{x}\), for \(x\ne0\). 3. The derivative formula is correct on the entire domain, but the stated identity is not. The expression \(4\ln x\) is defined only for \(x>0\), while \(\ln(x^4)\) is also defined for \(x<0\). A domain-valid identity is \(\ln(x^4)=4\ln|x|\) for \(x\ne0\).

Answer

a) \(D_f=\mathbb{R}\setminus\{0\}\) b) \(f'(x)=\frac{4}{x}\), for \(x\ne0\) c) The derivative result is correct, but the identity \(\ln(x^4)=4\ln x\) is valid only for \(x>0\). On the full domain, use \(\ln(x^4)=4\ln|x|\).
52761512
Let \(u(x)=e^x\), \(v(x)=\cos(x)\), and \(w(x)=x^2+3\). Write each function below as a combination of \(u\), \(v\), and \(w\) using addition, subtraction, multiplication, division, or composition. a) \(f_1(x)=e^{x^2+3}\cos(x)\) b) \(f_2(x)=\cos(x^2+3)+e^x\) c) \(f_3(x)=\frac{x^2+3}{e^x}\) Then find \(u'(x)\), \(v'(x)\), \(w'(x)\), \(f_1'(x)\), and \(f_2'(x)\).

Hints

- Distinguish between composing functions and combining their outputs arithmetically. - Identify the inner and outer functions in each composition. - Decide which rules are needed when functions are multiplied or added. - Find the derivatives of the three basic functions first.

Solution

1. The functions can be written as \(f_1(x)=(u\circ w)(x)v(x)\), \(f_2(x)=(v\circ w)(x)+u(x)\), and \(f_3(x)=\frac{w(x)}{u(x)}\). 2. The basic derivatives are \(u'(x)=e^x\), \(v'(x)=-\sin(x)\), and \(w'(x)=2x\). 3. For \(f_1\), use the chain rule and product rule: \(f_1'(x)=e^{x^2+3}(2x)\cos(x)+e^{x^2+3}(-\sin(x))\) \(=e^{x^2+3}(2x\cos(x)-\sin(x))\). 4. For \(f_2\), use the chain rule and sum rule: \(f_2'(x)=-\sin(x^2+3)(2x)+e^x\) \(=e^x-2x\sin(x^2+3)\).

Answer

a) \(f_1(x)=(u\circ w)(x)v(x)\) b) \(f_2(x)=(v\circ w)(x)+u(x)\) c) \(f_3(x)=\frac{w(x)}{u(x)}\) \(u'(x)=e^x\), \(v'(x)=-\sin(x)\), and \(w'(x)=2x\) \(f_1'(x)=e^{x^2+3}(2x\cos(x)-\sin(x))\) \(f_2'(x)=e^x-2x\sin(x^2+3)\)
52761612
Let \(a(x)=\ln(x)\), \(b(x)=\sqrt{x}\), and \(c(x)=5-x^2\). Write each function below as a combination of \(a\), \(b\), and \(c\). a) \(g_1(x)=\ln(5-x^2)\) b) \(g_2(x)=\sqrt{\ln(x)}\) c) \(g_3(x)=\frac{\sqrt{x}}{5-x^2}\) Then find \(a'(x)\), \(b'(x)\), \(c'(x)\), \(g_1'(x)\), and \(g_2'(x)\).

Hints

- Identify which function is used as the input to another function. - Use the chain rule: derivative of the outer function times derivative of the inner function. - Recall the derivatives of the natural logarithm and square root. - The third function has a quotient structure.

Solution

1. The functions can be written as \(g_1(x)=(a\circ c)(x)\), \(g_2(x)=(b\circ a)(x)\), and \(g_3(x)=\frac{b(x)}{c(x)}\). 2. The basic derivatives are \(a'(x)=\frac{1}{x}\), \(b'(x)=\frac{1}{2\sqrt{x}}\), and \(c'(x)=-2x\). 3. For \(g_1\), the chain rule gives \(g_1'(x)=\frac{1}{5-x^2}(-2x)=\frac{2x}{x^2-5}\). 4. For \(g_2\), the chain rule gives \(g_2'(x)=\frac{1}{2\sqrt{\ln(x)}}\left(\frac{1}{x}\right)=\frac{1}{2x\sqrt{\ln(x)}}\). The domains are \((-\sqrt{5}, \sqrt{5})\) for \(g_1\), \([1, \infty)\) for \(g_2\), and \([0, \sqrt{5})\cup(\sqrt{5}, \infty)\) for \(g_3\). The derivative \(g_2'\) is defined for \(x>1\).

Answer

a) \(g_1(x)=(a\circ c)(x)\) b) \(g_2(x)=(b\circ a)(x)\) c) \(g_3(x)=\frac{b(x)}{c(x)}\) \(a'(x)=\frac{1}{x}\), \(b'(x)=\frac{1}{2\sqrt{x}}\), and \(c'(x)=-2x\) \(g_1'(x)=\frac{2x}{x^2-5}\) for \(-\sqrt{5}<x<\sqrt{5}\) \(g_2'(x)=\frac{1}{2x\sqrt{\ln(x)}}\) for \(x>1\)
52762012
Let \(g(x)=\ln\left(\frac{4}{2x+1}\right)\), where \(x>-0.5\). Find the slope of the graph at \(x=1.5\).

Hints

- The slope at an input is the derivative value there. - Use the quotient property of logarithms before differentiating. - Include the inner derivative of \(2x+1\).

Solution

1. Rewrite the function: \(g(x)=\ln4-\ln(2x+1)\). 2. Differentiate using the chain rule: \(g'(x)=-\frac{2}{2x+1}\). 3. Evaluate at \(x=1.5\): \(g'(1.5)=-\frac{2}{2\cdot1.5+1}=-\frac{1}{2}\).

Answer

\(-\frac{1}{2}\)
52762212
Let \(g(x)=\ln(\ln x)\). Find the maximal domain of \(g\) and find \(g'(x)\).

Hints

- The input of the outer logarithm must be positive. - Determine when \(\ln x>0\). - Treat \(\ln x\) as the inner function. - Apply the chain rule step by step.

Solution

1. The outer logarithm requires \(\ln x>0\). This occurs when \(x>1\), which also satisfies the inner logarithm’s requirement \(x>0\). Thus, \(D_g=(1, \infty)\). 2. Apply the chain rule: \(g'(x)=\frac{1}{\ln x}\cdot\frac{1}{x}=\frac{1}{x\ln x}\).

Answer

\(D_g=(1, \infty)\) \(g'(x)=\frac{1}{x\ln x}\)
52762712
Find \(f'(x)\) for each function. State the domain of each derivative. a) \(f(x)=\ln(1-4x)\) b) \(f(x)=x^2\ln(5x)\)

Hints

- Identify the inner and outer functions in part a. - Recall the derivative of the natural logarithm. - Apply the product rule in part b. - Determine the logarithm domain separately for each part.

Solution

1. For part a, apply the chain rule: \(f'(x)=\frac{-4}{1-4x}=\frac{4}{4x-1}\). The logarithm requires \(1-4x>0\), so \(x<\frac{1}{4}\). 2. For part b, apply the product rule. Since \(\frac{d}{dx}\ln(5x)=\frac{1}{x}\), \(f'(x)=2x\ln(5x)+x^2\left(\frac{1}{x}\right)=2x\ln(5x)+x\). This expression is defined for \(x>0\).

Answer

a) \(f'(x)=\frac{4}{4x-1}\), for \(x<\frac{1}{4}\) b) \(f'(x)=2x\ln(5x)+x\), for \(x>0\)
52766412
Let \(u\) be differentiable on \(\mathbb{R}\). Wherever \(u(x)>0\), define \(g(x)=\ln(u(x))\). Decide whether each statement is true. (1) If \(x_0\) is a zero of \(u\), then \(x_0\) is also a zero of \(g\). (2) At every local extremum of \(u\) that lies in the domain of \(g\), the graph of \(g\) has a horizontal tangent. (3) If \(g(x_0)=0\), then \(u(x_0)=1\).

Hints

- Recall the domain restriction for a logarithm. - Use the chain rule to differentiate \(g\). - At a local extremum of \(u\), what is the value of \(u'\)? - Determine which logarithm input produces an output of \(0\).

Solution

1. Statement (1) is false. If \(u(x_0)=0\), then \(\ln(u(x_0))=\ln(0)\) is undefined, so \(x_0\) is not even in the domain of \(g\). 2. By the chain rule, \(g'(x)=\frac{u'(x)}{u(x)}\). At a local extremum \(x_0\) of \(u\), \(u'(x_0)=0\). Because \(x_0\) is in the domain of \(g\), \(u(x_0)>0\), so \(g'(x_0)=0\). Statement (2) is true. 3. If \(g(x_0)=0\), then \(\ln(u(x_0))=0\). Exponentiating gives \(u(x_0)=e^0=1\). Statement (3) is true.

Answer

(1) False (2) True (3) True
52767212
Let \(f(x)=\ln(x^2+4x+4)\). Find the maximal domain of \(f\) and find \(f'(x)\) in simplest form.

Hints

- Factor the quadratic inside the logarithm. - Determine where that expression is positive. - Apply the chain rule. - Cancel common factors only after preserving the domain restriction.

Solution

1. Factor the logarithm’s argument: \(x^2+4x+4=(x+2)^2\). This expression is positive for every real \(x\) except \(x=-2\). Thus, \(D_f=\mathbb{R}\setminus\{-2\}\). 2. Apply the chain rule: \(f'(x)=\frac{2x+4}{x^2+4x+4}\). Factor and simplify: \(f'(x)=\frac{2(x+2)}{(x+2)^2}=\frac{2}{x+2}\), for \(x\ne-2\).

Answer

\(D_f=\mathbb{R}\setminus\{-2\}\) \(f'(x)=\frac{2}{x+2}\)
52885212
Consider the family of functions \(f_k(x)=\sqrt{k-x^2}\), where \(k>0\). Each graph is the upper semicircle of a circle centered at the origin. a) Find \(k\) so that \(A(2, 4)\) lies on the graph. b) For the value of \(k\) from part a, find the equation of the tangent line at \(x=2\).

Hints

- Substitute the coordinates of the given point into the function. - Rewrite the square root as a power and apply the chain rule. - The derivative gives the tangent slope. - Use point-slope form for the tangent line.

Solution

1. Substitute \(A(2, 4)\): \(4=\sqrt{k-4}\). Squaring gives \(16=k-4\), so \(k=20\). 2. For \(f_{20}(x)=\sqrt{20-x^2}\), the chain rule gives \(f_{20}'(x)=-\frac{x}{\sqrt{20-x^2}}\). 3. The slope at \(x=2\) is \(f_{20}'(2)=-\frac{2}{4}=-\frac{1}{2}\). 4. Using point-slope form through \((2, 4)\), \(y-4=-\frac{1}{2}(x-2)\). Therefore, \(y=-\frac{1}{2}x+5\).

Answer

a) \(k=20\) b) \(y=-\frac{1}{2}x+5\)
52903612
Find \(f'(x)\) for each function. State the domain of each derivative. a) \(f(x)=\cos(5x+2)\) b) \(f(x)=-2\sin(0.4x)\) c) \(f(x)=\frac{1}{2}x^4-\sqrt{x}+\sin x\)

Hints

- Recall the derivatives of sine and cosine. - For a trigonometric function with a linear input, multiply by the derivative of the input. - Track the negative sign when differentiating cosine. - In part c, differentiate each term separately and check the square-root domain.

Solution

1. For part a, apply the chain rule: \(f'(x)=-\sin(5x+2)\cdot5=-5\sin(5x+2)\). This derivative is defined for all real \(x\). 2. For part b, apply the constant multiple rule and chain rule: \(f'(x)=-2\cdot0.4\cos(0.4x)=-0.8\cos(0.4x)\). This derivative is defined for all real \(x\). 3. For part c, differentiate term by term: \(f'(x)=2x^3-\frac{1}{2\sqrt{x}}+\cos x\). This derivative is defined for \(x>0\).

Answer

a) \(f'(x)=-5\sin(5x+2)\), for all real \(x\) b) \(f'(x)=-0.8\cos(0.4x)\), for all real \(x\) c) \(f'(x)=2x^3-\frac{1}{2\sqrt{x}}+\cos x\), for \(x>0\)
52949312
Let \(f(x)=\cos(x^2)\) for all real \(x\). 1) Use the chain rule to find \(f'(x)\). 2) Find the exact slope of the graph of \(f\) at \(x=\sqrt{\frac{\pi}{3}}\).

Hints

- Identify the inner and outer functions. - Apply the chain rule to differentiate the composition. - Use the exact sine value for the special angle in part 2.

Solution

1. The outer function is cosine, and the inner function is \(x^2\). By the chain rule, \(f'(x)=-\sin(x^2)(2x)=-2x\sin(x^2)\). 2. Substitute \(x=\sqrt{\frac{\pi}{3}}\): \(f'\left(\sqrt{\frac{\pi}{3}}\right)=-2\sqrt{\frac{\pi}{3}}\sin\left(\frac{\pi}{3}\right)\). Since \(\sin\left(\frac{\pi}{3}\right)=\frac{\sqrt{3}}{2}\), \(f'\left(\sqrt{\frac{\pi}{3}}\right)=-2 \cdot \sqrt{\frac{\pi}{3}} \cdot \left(\frac{\sqrt{3}}{2}\right)=-\sqrt{\pi}\).

Answer

1) \(f'(x)=-2x\sin(x^2)\) 2) The exact slope is \(-\sqrt{\pi}\).
52949412
Consider \(g(x)=\cos^2(x)\) on the interval \([0, \pi]\). 1) Identify an inner function \(v\) and an outer function \(u\) such that \(g(x)=u(v(x))\). 2) Find \(g'(x)\). 3) Find every \(x\in[0, \pi]\) where the graph of \(g\) has a horizontal tangent.

Hints

- A horizontal tangent has slope zero. - Identify which operation acts on \(x\) first and which acts on the result. - Use the unit circle or known zeros of sine and cosine.

Solution

1. One decomposition is \(v(x)=\cos(x)\) and \(u(t)=t^2\). 2. By the chain rule, \(g'(x)=2\cos(x)(-\sin(x))=-2\sin(x)\cos(x)\). Equivalently, \(g'(x)=-\sin(2x)\). 3. A horizontal tangent occurs where \(g'(x)=0\). Thus, \(-2\sin(x)\cos(x)=0\), so either \(\sin(x)=0\) or \(\cos(x)=0\). On \([0, \pi]\), these equations give \(x=0\), \(x=\frac{\pi}{2}\), and \(x=\pi\).

Answer

1) \(v(x)=\cos(x)\) and \(u(t)=t^2\) 2) \(g'(x)=-2\sin(x)\cos(x)=-\sin(2x)\) 3) \(x=0\), \(x=\frac{\pi}{2}\), and \(x=\pi\)
52950112
Let \(u(x)=\ln(x)\) for \(x>0\), \(v(x)=\sqrt{x}\) for \(x\ge 0\), and \(w(x)=x^2+5\) for all real \(x\). 1) Write a formula for \(f(x)=u(v(w(x)))\). 2) Use the chain rule to find \(f'(x)\).

Hints

- Evaluate the composition from the inside out. - Apply the chain rule once for each layer of the composition. - The derivative is the product of the derivative factors from the outermost function to the innermost function. - A logarithm property can provide a useful check.

Solution

1. Work from the inside out: \(v(w(x))=\sqrt{x^2+5}\), so \(f(x)=\ln\left(\sqrt{x^2+5}\right)\). Equivalently, \(f(x)=\frac{1}{2}\ln(x^2+5)\). 2. Applying the chain rule to all three layers gives \(f'(x)=\frac{1}{\sqrt{x^2+5}}\left(\frac{1}{2\sqrt{x^2+5}}\right)(2x)\) \(=\frac{x}{x^2+5}\).

Answer

1) \(f(x)=\ln\left(\sqrt{x^2+5}\right)=\frac{1}{2}\ln(x^2+5)\) 2) \(f'(x)=\frac{x}{x^2+5}\)
52950212
Consider \(h(x)=\cos^4(3x-1)\). 1) Identify functions \(u\), \(v\), and \(w\) such that \(h(x)=u(v(w(x)))\). 2) Find \(h'(x)\).

Hints

- List the operations in the order in which they are performed on an input. - Recall that \(\cos^4(z)\) means \((\cos(z))^4\). - Remember the negative sign in the derivative of cosine. - Combine the constant factors after applying the chain rule.

Solution

1. One decomposition is \(w(x)=3x-1\), \(v(t)=\cos(t)\), and \(u(t)=t^4\). 2. Apply the chain rule through all three layers: \(h'(x)=4\cos^3(3x-1)[-\sin(3x-1)]\cdot 3\) \(=-12\cos^3(3x-1)\sin(3x-1)\).

Answer

1) \(w(x)=3x-1\), \(v(t)=\cos(t)\), and \(u(t)=t^4\) 2) \(h'(x)=-12\cos^3(3x-1)\sin(3x-1)\)
52950512
Let \(p(x)=e^x\), \(q(x)=x^2-4\), and \(r(x)=\cos(x)\). a) Write a formula for the composition \(f(x)=p(q(r(x)))\). b) Use the chain rule to find \(f'(x)\).

Hints

- Build the composition from the innermost function outward. - Substitute the entire output of one function into the next function. - Apply the chain rule once for each nested layer. - Recall the derivatives of cosine and the exponential function.

Solution

1. First, \(q(r(x))=\cos^2(x)-4\). Therefore, \(f(x)=e^{\cos^2(x)-4}\). 2. Differentiate the exponent using the chain rule: \(\frac{d}{dx}[\cos^2(x)-4]=2\cos(x)(-\sin(x))=-2\sin(x)\cos(x)\). 3. Apply the chain rule to the exponential function: \(f'(x)=-2\sin(x)\cos(x)e^{\cos^2(x)-4}\). Since \(2\sin(x)\cos(x)=\sin(2x)\), this can also be written as \(f'(x)=-\sin(2x)e^{\cos^2(x)-4}\).

Answer

a) \(f(x)=e^{\cos^2(x)-4}\) b) \(f'(x)=-2\sin(x)\cos(x)e^{\cos^2(x)-4}=-\sin(2x)e^{\cos^2(x)-4}\)
52951212
Find the derivative of \(g(x)=\sqrt{e^{x^2+4}}\) by treating it as a composition of three functions.

Hints

- Describe the function as three operations performed in sequence. - Recall the derivatives of the square-root and exponential functions. - Simplify after multiplying the three derivative factors. - Rewrite the expression using exponent rules to check your result.

Solution

1. One decomposition is \(u(t)=\sqrt{t}\), \(v(t)=e^t\), and \(w(x)=x^2+4\). 2. Their derivatives are \(u'(t)=\frac{1}{2\sqrt{t}}\), \(v'(t)=e^t\), and \(w'(x)=2x\). 3. By the chain rule, \(g'(x)=\frac{1}{2\sqrt{e^{x^2+4}}}e^{x^2+4}(2x)\) \(=x\sqrt{e^{x^2+4}}\). 4. As a check, \(g(x)=e^{\frac{1}{2}x^2+2}\), whose derivative is \(g'(x)=xe^{\frac{1}{2}x^2+2}\), the same result.

Answer

\(g'(x)=x\sqrt{e^{x^2+4}}=xe^{\frac{1}{2}x^2+2}\)
52951512
Let \(u\) and \(v\) be polynomial functions with degrees \(n\) and \(m\), respectively, where \(n,m\ge1\). Define \(f(x)=u(v(x))\). 1) Find the degree of \(f\) in terms of \(n\) and \(m\). 2) Find the degree of \(f'\). 3) For which values of \(n\) and \(m\) does \(f\) have the same degree as \(h(x)=u(x)v(x)\)?

Hints

- Use the degree rule for polynomial composition. - Differentiating a nonconstant polynomial lowers its degree by \(1\). - The degree of a product is the sum of the degrees. - Factor the equation obtained by equating the two degrees.

Solution

1. The degree of a polynomial composition is the product of the degrees, so \(\deg(f)=nm\). 2. A nonconstant polynomial of degree \(nm\) has a derivative of degree \(nm-1\). This also follows from the chain rule: \(f'(x)=u'(v(x))v'(x)\), whose factors have degrees \((n-1)m\) and \(m-1\), for a total of \(nm-1\). 3. The product \(h(x)=u(x)v(x)\) has degree \(n+m\). Equating the degrees gives \(nm=n+m\), or \((n-1)(m-1)=1\). Since \(n\) and \(m\) are positive integers, the only solution is \(n=m=2\).

Answer

1) \(\deg(f)=nm\) 2) \(\deg(f')=nm-1\) 3) \(n=2\) and \(m=2\)
52951612
A polynomial function \(f\) is defined by \(f=p\circ q\), where \(p\) and \(q\) are polynomial functions. The derivative \(f'\) has degree \(11\). Use the chain rule and polynomial degrees to find all possible ordered pairs \((n, m)\), where \(n=\deg(p)\) and \(m=\deg(q)\), given that \(n,m\ge2\).

Hints

- Apply the chain rule to \(f=p\circ q\). - Find the degree of each factor in \(f'(x)=p'(q(x))q'(x)\). - List the ordered factor pairs that satisfy the restrictions.

Solution

1. By the chain rule, \(f'(x)=p'(q(x))q'(x)\). The factors have degrees \((n-1)m\) and \(m-1\), so \(\deg(f')=(n-1)m+(m-1)=nm-1\). 2. Since \(f'\) has degree \(11\), \(nm-1=11\), so \(nm=12\). 3. The ordered factor pairs of \(12\) with both entries at least \(2\) are \((2, 6)\), \((3, 4)\), \((4, 3)\), and \((6, 2)\).

Answer

\((2, 6)\), \((3, 4)\), \((4, 3)\), and \((6, 2)\)
52952012
Find the slope of the graph of each function at the given value \(x_0\). a) \(f(x)=\sqrt{x^2+9}\) at \(x_0=4\) b) \(f(x)=\sin(2x)\) at \(x_0=\frac{\pi}{6}\) c) \(f(x)=(\cos(x)+1)^3\) at \(x_0=\frac{\pi}{2}\)

Hints

- First find the derivative using the chain rule. - The slope at a point is the value of the first derivative there. - Use radians for the trigonometric inputs. - Treat the power in part c as the outer function.

Solution

1. For a), \(f'(x)=\frac{x}{\sqrt{x^2+9}}\), so \(f'(4)=\frac{4}{\sqrt{25}}=\frac{4}{5}=0.8\). 2. For b), \(f'(x)=2\cos(2x)\), so \(f'\left(\frac{\pi}{6}\right)=2\cos\left(\frac{\pi}{3}\right)=1\). 3. For c), \(f'(x)=3(\cos(x)+1)^2(-\sin(x))\), so \(f'\left(\frac{\pi}{2}\right)=3\cdot 1^2\cdot(-1)=-3\).

Answer

a) \(f'(4)=0.8\) b) \(f'\left(\frac{\pi}{6}\right)=1\) c) \(f'\left(\frac{\pi}{2}\right)=-3\)
52952112
Let \(f(x)=(0.5x^2-2)^3\). 1) Find \(f'(x)\) using the chain rule. 2) Find \(f'(x)\) another way by expanding the original expression and differentiating term by term. 3) Show that the two results are equivalent.

Hints

- Identify the inner and outer functions. - Expand the cube by multiplying or using the binomial theorem. - Expand or factor one derivative expression to compare the two forms.

Solution

1. Using the chain rule, \(f'(x)=3(0.5x^2-2)^2(x)=3x(0.5x^2-2)^2\). 2. Expanding first gives \(f(x)=0.125x^6-1.5x^4+6x^2-8\). Therefore, \(f'(x)=0.75x^5-6x^3+12x\). 3. Expand the chain-rule result: \(3x(0.5x^2-2)^2=3x(0.25x^4-2x^2+4)\) \(=0.75x^5-6x^3+12x\). Thus, the results are equivalent.

Answer

1) \(f'(x)=3x(0.5x^2-2)^2\) 2) \(f'(x)=0.75x^5-6x^3+12x\) 3) Expanding the first expression gives the second expression.
52952212
Use the chain rule to find and simplify the derivative of each function. a) \(g(x)=\sqrt{x^2+2x+5}\) b) \(h(x)=\frac{10}{(3x-1)^4}\) c) \(k(x)=\sqrt{2x}+(x^3-1)^2\)

Hints

- Rewrite radicals as fractional powers when useful. - A fraction with a constant numerator can be rewritten using a negative exponent. - Differentiate the terms of a sum separately.

Solution

1. For a), \(g'(x)=\frac{1}{2\sqrt{x^2+2x+5}}(2x+2)\) \(=\frac{x+1}{\sqrt{x^2+2x+5}}\). This derivative is defined for all real \(x\). 2. For b), rewrite \(h(x)=10(3x-1)^{-4}\). Then \(h'(x)=10[-4(3x-1)^{-5}]\cdot 3\) \(=-\frac{120}{(3x-1)^5}\), which is defined for \(x\ne\frac{1}{3}\). 3. For c), differentiate each term: \(k'(x)=\frac{1}{2\sqrt{2x}}\cdot 2+2(x^3-1)(3x^2)\) \(=\frac{1}{\sqrt{2x}}+6x^2(x^3-1)\). This derivative is defined for \(x>0\).

Answer

a) \(g'(x)=\frac{x+1}{\sqrt{x^2+2x+5}}\), for all real \(x\) b) \(h'(x)=-\frac{120}{(3x-1)^5}\), for \(x\ne\frac{1}{3}\) c) \(k'(x)=\frac{1}{\sqrt{2x}}+6x^2(x^3-1)\), for \(x>0\)
52955412
Consider the family \(f_k(x)=\sqrt{kx-\frac{1}{4}x^2}\), where \(k>0\). a) Find the point common to all graphs. b) Show that each graph has a local maximum, and find its coordinates in terms of \(k\). c) Find the equation of the line containing all of these local maxima.

Hints

- First determine the domain of each square-root function. - Use the chain rule on the square root. - The sign of the derivative is controlled by its numerator. - Eliminate \(k\) from the maximum coordinates.

Solution

1. The radicand is nonnegative on \([0, 4k]\). Every graph contains \((0, 0)\). If a point with \(x\neq0\) were common to graphs with distinct parameters \(k\) and \(m\), then \(kx-\frac{x^2}{4}=mx-\frac{x^2}{4}\), which would imply \(k=m\). Thus the origin is the only common point. 2. For interior points of the domain, the chain rule gives \(f_k'(x)=\frac{k-x/2}{2\sqrt{kx-x^2/4}}\). The derivative is zero at \(x=2k\), positive before this point, and negative after it, so the graph has a local maximum there. 3. Its y-coordinate is \(f_k(2k)=\sqrt{2k^2-k^2}=k\). Therefore, the local maximum is \((2k, k)\). 4. Since \(x=2k\) and \(y=k\), all maxima lie on \(y=\frac{1}{2}x\).

Answer

a) \((0, 0)\) b) \((2k, k)\) c) \(y=\frac{1}{2}x\)
52990112
Let \(f(x)=4e^{-0.25x}\). 1. Find the equation of the tangent line \(t\) to the graph of \(f\) at \(x_0=4\). 2. Find the x- and y-intercepts of \(t\). 3. The tangent line and the coordinate axes form a right triangle. Find its area.

Hints

- Find the point and slope needed for a tangent-line equation. - Use point-slope form at \(x_0=4\). - Apply the chain rule when differentiating the exponential function. - Set \(y=0\) for the x-intercept and \(x=0\) for the y-intercept. - Use the intercept distances as the legs of the right triangle.

Solution

1. Evaluate the function: \(f(4)=4e^{-1}=\frac{4}{e}\). Differentiate using the chain rule: \(f'(x)=-e^{-0.25x}\), so \(f'(4)=-\frac{1}{e}\). 2. Use point-slope form: \(y-\frac{4}{e}=-\frac{1}{e}(x-4)\). Therefore, \(t: y=-\frac{1}{e}x+\frac{8}{e}\). 3. For the y-intercept, set \(x=0\), giving \(\left(0, \frac{8}{e}\right)\). For the x-intercept, set \(y=0\), giving \(x=8\), so the intercept is \((8, 0)\). 4. The triangle has legs \(8\) and \(\frac{8}{e}\). Its area is \(A=\frac{1}{2}\cdot8\cdot\frac{8}{e}=\frac{32}{e}\approx11.77\) square units.

Answer

1. \(t: y=-\frac{1}{e}x+\frac{8}{e}\) 2. x-intercept: \((8, 0)\); y-intercept: \(\left(0, \frac{8}{e}\right)\) 3. \(A=\frac{32}{e}\approx11.77\) square units
52990212
Consider the family of functions \(f_k(x)=e^{kx}\), where \(k\neq0\). 1. Show algebraically that the tangent line at any point \(x_0\) crosses the x-axis at \(x_s=x_0-\frac{1}{k}\). 2. Find \(k\) so that the tangent line at \(x_0=3\) crosses the x-axis at \(x_s=1\). 3. For \(k=0.5\), at what value of \(x_0\) must the tangent line be drawn so that it passes through the origin?

Hints

- Work with \(x_0\) and \(k\) symbolically in part 1. - At an x-intercept, the y-coordinate is \(0\). - Factor out \(e^{kx_0}\) from the intercept equation. - Use the result from part 1 for parts 2 and 3. - The origin has x-coordinate \(0\).

Solution

1. Differentiate: \(f_k'(x)=ke^{kx}\). The tangent line at \(x_0\) is \(y=ke^{kx_0}(x-x_0)+e^{kx_0}\). 2. At the x-intercept, \(y=0\). Thus \(0=e^{kx_0}[k(x_s-x_0)+1]\). Since \(e^{kx_0}>0\), \(k(x_s-x_0)+1=0\), so \(x_s=x_0-\frac{1}{k}\). 3. Substitute \(x_0=3\) and \(x_s=1\): \(1=3-\frac{1}{k}\). Therefore, \(\frac{1}{k}=2\), so \(k=0.5\). 4. A line through the origin has x-intercept \(x_s=0\). With \(k=0.5\), \(0=x_0-\frac{1}{0.5}=x_0-2\), so \(x_0=2\).

Answer

1. \(x_s=x_0-\frac{1}{k}\) 2. \(k=0.5\) 3. \(x_0=2\)
52996212
Find the points on the graph of \(f(x)=\ln(x^2+1)\) where the tangent line is parallel to \(4x-5y+10=0\). Find the equations of those tangent lines.

Hints

- Parallel lines have the same slope. - Use the chain rule to differentiate the logarithmic function. - Setting the derivative equal to the line's slope produces a quadratic equation. - Use point-slope form for each tangent line.

Solution

1. Rewrite the given line as \(y=\frac{4}{5}x+2\), so its slope is \(\frac{4}{5}\). 2. Differentiate using the chain rule: \(f'(x)=\frac{2x}{x^2+1}\). 3. Set the derivative equal to the required slope: \(\frac{2x}{x^2+1}=\frac{4}{5}\). This gives \(4x^2-10x+4=0\), or \(2x^2-5x+2=0\). 4. Factor: \((2x-1)(x-2)=0\). Thus \(x=\frac{1}{2}\) or \(x=2\). 5. The corresponding points are \(P_1\left(\frac{1}{2}, \ln\left(\frac{5}{4}\right)\right)\) and \(P_2(2, \ln 5)\). 6. Using slope \(\frac{4}{5}\), the tangent lines are \(y-\ln\left(\frac{5}{4}\right)=\frac{4}{5}\left(x-\frac{1}{2}\right)\) and \(y-\ln 5=\frac{4}{5}(x-2)\).

Answer

Points: \(P_1\left(\frac{1}{2}, \ln\left(\frac{5}{4}\right)\right)\) and \(P_2(2, \ln 5)\) Tangent lines: \(y=\frac{4}{5}x-\frac{2}{5}+\ln\left(\frac{5}{4}\right)\) and \(y=\frac{4}{5}x-\frac{8}{5}+\ln 5\)
53001412
Let \(f(x)=\ln(x^2)\) for \(x\neq0\). a) Show that exactly two tangent lines to the graph of \(f\) pass through the origin. b) Find the equations of those tangent lines.

Hints

- A line through the origin has equation \(y=mx\). - At the point of tangency, the line's slope equals the derivative. - Use the chain rule to differentiate \(\ln(x^2)\). - Determine how many solutions the equation for \(u\) has.

Solution

1. Differentiate using the chain rule: \(f'(x)=\frac{2}{x}\). 2. Let the point of tangency have x-coordinate \(u\neq0\). A tangent line through the origin has slope \(\frac{2}{u}\), so its equation is \(y=\frac{2}{u}x\). 3. The point \((u, \ln(u^2))\) must lie on this line. Therefore, \(\ln(u^2)=\frac{2}{u}u=2\). 4. Solving \(\ln(u^2)=2\) gives \(u^2=e^2\), so \(u=e\) or \(u=-e\). These are the only two solutions, so exactly two such tangent lines exist. 5. Their slopes are \(\frac{2}{e}\) and \(-\frac{2}{e}\). Thus the tangent lines are \(y=\frac{2}{e}x\) and \(y=-\frac{2}{e}x\).

Answer

a) The two points of tangency occur at \(u=e\) and \(u=-e\). b) \(y=\frac{2}{e}x\) and \(y=-\frac{2}{e}x\)
53261212
The graph of a quadratic function \(f\), defined for all real numbers, is shown. The graph has a horizontal tangent only at \(x=4\). Define \(h(x)=f(x^2+3)\). a) Use the graph to find \(f(2)\) and \(f(4)\), and then find \(h(1)\). b) Use the chain rule to find \(h'(x)\). Then use the graph to find every point where the graph of \(h\) has a horizontal tangent.
Figure for problem 532612

Hints

- Evaluate a composition from the inside out. - Use the chain rule for a function of the form \(f(g(x))\). - A horizontal tangent occurs where the derivative is zero. - Use the zero-product property on the two derivative factors.

Solution

1. From the graph, \(f(2)=3\) and \(f(4)=4\). Therefore, \(h(1)=f(1^2+3)=f(4)=4\). 2. By the chain rule, \(h'(x)=2x f'(x^2+3)\). 3. A horizontal tangent occurs where \(2x f'(x^2+3)=0\). One possibility is \(2x=0\), which gives \(x=0\). The graph of \(f\) has a horizontal tangent only when its input is \(4\), so the other possibility is \(x^2+3=4\). Thus, \(x^2=1\), giving \(x=-1\) or \(x=1\). Therefore, the graph of \(h\) has horizontal tangents at \(x=-1\), \(x=0\), and \(x=1\).

Answer

a) \(f(2)=3\), \(f(4)=4\), and \(h(1)=4\) b) \(h'(x)=2x f'(x^2+3)\); the horizontal tangents occur at \(x=-1\), \(x=0\), and \(x=1\).
53265012
Let \(f(x)=\frac{8}{x^2+4}\). Its graph is shown. a) Find an equation of the tangent line \(t\) at \(P(2,f(2))\). b) Find the acute angle at which \(t\) intersects the x-axis. Round to the nearest tenth of a degree.
Figure for problem 532650

Hints

- Evaluate \(f(2)\) to find the point of tangency. - Rewrite the function with a negative exponent and apply the chain rule. - The derivative value at \(x=2\) is the tangent slope. - Use point-slope form for the tangent line. - Use the absolute value of the slope when finding the acute angle with the x-axis.

Solution

1. Find the point of tangency: \(f(2)=\frac{8}{2^2+4}=1\), so \(P=(2,1)\). 2. Differentiate using the chain rule: \(f'(x)=-\frac{16x}{(x^2+4)^2}\). 3. The tangent slope is \(f'(2)=-\frac{32}{64}=-0.5\). 4. Use point-slope form: \(y-1=-0.5(x-2)\), so \(y=-0.5x+2\). 5. For the acute angle \(\beta\), use \(\tan(\beta)=|-0.5|\). Thus, \(\beta=\arctan(0.5)\approx26.6^\circ\).

Answer

a) \(t: y=-0.5x+2\) b) \(\beta\approx26.6^\circ\)
53444212
Let \(h(x)=\sin(2x)\). The graph of \(h\) and the graph of its derivative are labeled I and II. a) Find \(h^{\prime}(x)\). b) Use the amplitudes to identify which graph represents \(h\) and which represents \(h^{\prime}\). c) On \([0, \pi]\), find the x-values where \(h\) has its greatest slope and state that maximum slope.
Figure for problem 534442

Hints

- Apply the chain rule to \(\sin(kx)\). - Compare the maximum vertical distances from the midline. - The greatest slope of the original function is the maximum value of its derivative.

Solution

1. By the chain rule, \(h^{\prime}(x)=2\cos(2x)\). 2. The function \(h(x)=\sin(2x)\) has amplitude \(1\), while \(h^{\prime}(x)=2\cos(2x)\) has amplitude \(2\). Therefore, Graph I represents \(h\), and Graph II represents \(h^{\prime}\). 3. The greatest slope of \(h\) is the maximum value of \(h^{\prime}(x)\). Since \(2\cos(2x)\le2\), the maximum slope is \(2\). 4. On \([0, \pi]\), \(\cos(2x)=1\) at \(x=0\) and \(x=\pi\).

Answer

a) \(h^{\prime}(x)=2\cos(2x)\) b) Graph I is \(h\); Graph II is \(h^{\prime}\). c) The maximum slope is \(2\), attained at \(x=0\) and \(x=\pi\).
53445312
The graphs of functions \(u\) and \(v\), together with a tangent to \(u\), are shown. Let \(f=u\circ v\), so \(f(x)=u(v(x))\). a) Use the graphs to find \(f(1)\) and \(f^{\prime}(1)\). b) The tangent line to \(f\) at \((1, f(1))\) forms a triangle with the coordinate axes. Find the area of the triangle.
Figure for problem 534453

Hints

- Evaluate the inner function first, then use its output as the input of the outer function. - Apply the chain rule \(f^{\prime}(x)=u^{\prime}(v(x))v^{\prime}(x)\). - Read each required slope from the line or tangent shown. - Use point-slope form to write the tangent equation.

Solution

1. From the graph, \(v(1)=2\), and then \(u(2)=-1\). Therefore, \(f(1)=u(v(1))=-1\). 2. By the chain rule, \(f^{\prime}(1)=u^{\prime}(v(1))v^{\prime}(1)=u^{\prime}(2)v^{\prime}(1)\). 3. The graph of \(v\) is a line with slope \(1\), so \(v^{\prime}(1)=1\). The displayed tangent to \(u\) at \(x=2\) has slope \(1\), so \(u^{\prime}(2)=1\). Thus, \(f^{\prime}(1)=1\). 4. The tangent through \((1, -1)\) with slope \(1\) is \(y+1=x-1\), or \(y=x-2\). 5. Its intercepts are \((2, 0)\) and \((0, -2)\). The triangle has area \(\frac{1}{2}\cdot2\cdot2=2\) square units.

Answer

a) \(f(1)=-1\) and \(f^{\prime}(1)=1\) b) \(2\) square units
53445812
The graph of a polynomial function \(f\), defined for all real numbers, is shown. Define \(g(x)=(f(x))^2\). Find every value of \(x\) where the graph of \(g\) has a horizontal tangent. Justify your reasoning using the chain rule.
Figure for problem 534458

Hints

- A horizontal tangent occurs where the derivative is zero. - Apply the chain rule to the square of a function. - Look for both zeros of \(f\) and points where the graph of \(f\) has a horizontal tangent.

Solution

1. By the chain rule, \(g'(x)=2f(x)f'(x)\). 2. A horizontal tangent occurs where \(g'(x)=0\). By the zero-product property, this happens when \(f(x)=0\) or \(f'(x)=0\). 3. The graph shows that \(f(x)=0\) at \(x=1\) and \(x=5\). 4. The graph of \(f\) has a horizontal tangent at its vertex, \(x=3\), so \(f'(3)=0\). Therefore, the graph of \(g\) has horizontal tangents at \(x=1\), \(x=3\), and \(x=5\).

Answer

The horizontal tangents occur at \(x=1\), \(x=3\), and \(x=5\).
53446212
The graph shows a radical function \(u\), a quadratic function \(v\), and tangents at the needed points. Define \(f(x)=u(v(x))\). a) Use the graph to find \(f(1)\). Give another x-value with the same function value. b) Find the equation of the tangent line to \(f\) at \((1, f(1))\). Then find the area of the triangle formed by this tangent and the coordinate axes.
Figure for problem 534462

Hints

- Evaluate the inner function before the outer function. - Find another x-value where the inner function has the same output. - Use the chain rule to find the tangent slope. - Check the tangent’s intercepts before calculating the triangle’s area.

Solution

1. From the graph, \(v(1)=1\), so \(f(1)=u(v(1))=u(1)=1\). 2. The graph of \(v\) also has \(v(3)=1\), so \(f(3)=u(1)=1\). 3. By the chain rule, \(f^{\prime}(1)=u^{\prime}(v(1))v^{\prime}(1)=u^{\prime}(1)v^{\prime}(1)\). 4. The tangent to \(u\) has slope \(\frac{1}{2}\), and the tangent to \(v\) at \(x=1\) has slope \(-1\). Thus, \(f^{\prime}(1)=\frac{1}{2}\cdot(-1)=-0.5\). 5. The tangent through \((1, 1)\) is \(y-1=-0.5(x-1)\), or \(y=-0.5x+1.5\). 6. Its intercepts are \((3, 0)\) and \((0, 1.5)\), so the triangle’s area is \(\frac{1}{2}\cdot3\cdot1.5=2.25\) square units.

Answer

a) \(f(1)=1\); another x-value is \(x=3\). b) The tangent is \(y=-0.5x+1.5\), and the area is \(2.25\) square units.
53446312
The figure shows the graphs of a quadratic function \(u\) and a linear function \(v\). Define \(f(x)=u(v(x))\). a) Use the graphs to find \(f(1)\) and a second value \(x\ne1\) for which \(f(x)=f(1)\). b) The tangent line to \(f\) at \(P(1,f(1))\) forms a triangle with the coordinate axes. Find the area of the triangle.
Figure for problem 534463

Hints

- Evaluate the inner graph first. - Find all inputs of \(u\) that produce the same output. - Use the chain rule for the tangent slope. - Find the tangent line intercepts before computing the triangle area.

Solution

1. The graph gives \(v(1)=2\) and \(u(2)=0\), so \(f(1)=0\). 2. The zeros of \(u\) occur at inputs \(0\) and \(2\). Besides \(v(1)=2\), the graph gives \(v(3)=0\). Therefore, the second value is \(x=3\). 3. By the chain rule, \(f'(x)=u'(v(x))v'(x)\). From the graphs, \(v'(x)=-1\) and \(u'(2)=2\), so \(f'(1)=-2\). 4. The tangent line through \((1, 0)\) is \(y=-2(x-1)=-2x+2\). Its intercepts are \((1, 0)\) and \((0, 2)\). The triangle area is \(\frac{1}{2}\cdot1\cdot2=1\).

Answer

a) \(f(1)=0\); the second value is \(x=3\). b) \(1\) square unit
53446412
Let \(f(x)=e^{0.5x}\), and let \(P(a, f(a))\) be any point on its graph. A tangent line \(t\) is drawn at \(P\). a) Find the equation of \(t\) in terms of \(a\). b) The tangent line crosses the x-axis at \(Q\). Find the x-coordinate of \(Q\) in terms of \(a\). c) Show algebraically that the horizontal distance from \(P\) to \(Q\), called the subtangent, is always \(2\). Check the result using the figure.
Figure for problem 534464

Hints

- Use point-slope form at \(x=a\). - At an x-intercept, the y-coordinate is \(0\). - Divide by the nonzero exponential factor. - The horizontal distance is the absolute difference of the x-coordinates.

Solution

1. Differentiate: \(f'(x)=0.5e^{0.5x}\). 2. The tangent line at \(x=a\) is \(t: y=0.5e^{0.5a}(x-a)+e^{0.5a}\). 3. At the x-intercept \(Q(x_Q, 0)\), \(0=0.5e^{0.5a}(x_Q-a)+e^{0.5a}\). Since \(e^{0.5a}>0\), divide by it to get \(0=0.5(x_Q-a)+1\). 4. Solving gives \(x_Q=a-2\). 5. The horizontal distance is \(|a-x_Q|=|a-(a-2)|=2\), independent of \(a\). In the figure, \(a=2\), so \(P=(2,e)\) and \(Q=(0,0)\), which are \(2\) units apart horizontally.

Answer

a) \(t: y=0.5e^{0.5a}(x-a)+e^{0.5a}\) b) \(x_Q=a-2\) c) \(|a-(a-2)|=2\), so the subtangent is always \(2\).
53451012
Let \(f(x)=4e^{-x^2/2}\). Its graph is shown. a) Find the y-intercept. b) Show algebraically that the graph has y-axis symmetry. c) Find an equation of the tangent line \(t\) at \(x=1\). d) Find the x-intercept of \(t\).
Figure for problem 534510

Hints

- A point on the y-axis has x-coordinate \(0\). - Compare \(f(-x)\) with \(f(x)\). - Use the chain rule to find the tangent slope. - Apply point-slope form for the tangent line. - An x-intercept has y-coordinate \(0\).

Solution

1. Since \(f(0)=4\), the y-intercept is \((0,4)\). 2. Since \(f(-x)=4e^{-(-x)^2/2}=4e^{-x^2/2}=f(x)\), the function is even and its graph has y-axis symmetry. 3. By the chain rule, \(f'(x)=-4xe^{-x^2/2}\). At \(x=1\), the slope is \(-4e^{-1/2}\), and the point of tangency is \((1,4e^{-1/2})\). Therefore, \(y-4e^{-1/2}=-4e^{-1/2}(x-1)\), so \(t(x)=-4e^{-1/2}x+8e^{-1/2}\). 4. Set \(t(x)=0\): \(-4e^{-1/2}x+8e^{-1/2}=0\), which gives \(x=2\).

Answer

a) \((0,4)\). b) \(f(-x)=f(x)\), so the graph has y-axis symmetry. c) \(t(x)=-4e^{-1/2}x+8e^{-1/2}\). d) \(x=2\).
53452612
The graph shows a quadratic function \(f\). Define \(g(x)=e^{f(x)}\). a) State the domain of \(g\). b) Determine the range of \(g\). c) Use the graph of \(f\) to describe where \(g\) is increasing and decreasing.
Figure for problem 534526

Hints

- What values can \(f(x)\) take according to the graph? - How does the increasing function \(e^u\) transform inequalities between exponent values? - In the chain rule, which factor determines the sign of \(g'(x)\)?

Solution

1. The quadratic function \(f\) is defined for every real number, and \(e^u\) is defined for every real input \(u\). Therefore, the domain of \(g\) is \(\mathbb{R}\). 2. From the graph, \(f\) has a maximum value of \(1\) at \(x=0\), and \(f(x)\to-\infty\) as \(|x|\to\infty\). Because the exponential function is strictly increasing, \(g(x)\leq e\), and \(g(x)>0\). Thus, the range is \((0, e]\). 3. The graph of \(f\) increases for \(x<0\) and decreases for \(x>0\). Since \(e^u\) preserves order, \(g\) has the same monotonicity: it increases on \((-\infty, 0]\) and decreases on \([0, \infty)\). 4. Equivalently, \(g'(x)=f'(x)e^{f(x)}\), and the exponential factor is always positive, so the sign of \(g'\) is the sign of \(f'\).

Answer

a) \(\mathbb{R}\) b) \((0, e]\) c) Increasing on \((-\infty, 0]\) and decreasing on \([0, \infty)\)
52582212
Let \(f(x)=\sin(x)\) and \(g(x)=mx+c\), where \(m,c\in\mathbb{R}\) and \(m>0\). 1. Write formulas for \(h_1(x)=f(g(x))\) and \(h_2(x)=g(f(x))\). 2. Use the chain rule to find \(h_1'(x)\) and \(h_2'(x)\). 3. The function \(h_1\) is sinusoidal. Explain how \(m\) and \(c\) affect its graph compared with \(f(x)=\sin(x)\), including its period. 4. Find \(m\) and \(c\) so that the range of \(h_2\) is \([-2, 4]\).

Hints

- Identify the inner and outer functions in each composition. - Use the chain rule: derivative of the outer function times derivative of the inner function. - Recall how the parameters in \(a\sin(bx+c)+d\) affect amplitude, period, and shifts. - Use the minimum and maximum values of sine to determine the range.

Solution

1. The compositions are \(h_1(x)=\sin(mx+c)\) and \(h_2(x)=m\sin(x)+c\). 2. By the chain rule, \(h_1'(x)=m\cos(mx+c)\) and \(h_2'(x)=m\cos(x)\). 3. The amplitude of \(h_1\) remains \(1\). Its period is \(\frac{2\pi}{m}\). Since \(mx+c=m\left(x+\frac{c}{m}\right)\), the graph is shifted horizontally by \(-\frac{c}{m}\): left when \(c>0\) and right when \(c<0\). 4. Since \(-1\le \sin(x)\le 1\) and \(m>0\), the range of \(h_2\) is \([c-m, c+m]\). Set the endpoints equal to the required range: \(c-m=-2\), \(c+m=4\). Adding gives \(2c=2\), so \(c=1\). Then \(m=3\).

Answer

1. \(h_1(x)=\sin(mx+c)\); \(h_2(x)=m\sin(x)+c\) 2. \(h_1'(x)=m\cos(mx+c)\); \(h_2'(x)=m\cos(x)\) 3. The period is \(\frac{2\pi}{m}\), the amplitude is \(1\), and the horizontal shift is \(-\frac{c}{m}\). 4. \(m=3\) and \(c=1\)
52592812
Let \(f\) be differentiable and odd, and define \(h(x)=\sin(f(x))\). a) Show that \(h\) is also odd. b) Use the chain rule to find \(h'(x)\). c) Differentiate the identity \(f(-x)=-f(x)\) to determine the symmetry of \(f'\). Then use your result to show that \(h'\) is even.

Hints

- Use the identity \(\sin(-z)=-\sin(z)\). - Remember the inner derivative when differentiating \(f(-x)\). - Recall the symmetry identity for cosine. - Consider how the product of two even functions behaves.

Solution

1. Since \(f\) is odd, \(f(-x)=-f(x)\). Therefore, \(h(-x)=\sin(f(-x))=\sin(-f(x))=-\sin(f(x))=-h(x)\). Thus, \(h\) is odd. 2. By the chain rule, \(h'(x)=\cos(f(x))f'(x)\). 3. Differentiate \(f(-x)=-f(x)\) with respect to \(x\): \(-f'(-x)=-f'(x)\). Hence, \(f'(-x)=f'(x)\), so \(f'\) is even. 4. Now, \(h'(-x)=\cos(f(-x))f'(-x)\) \(=\cos(-f(x))f'(x)\) \(=\cos(f(x))f'(x)=h'(x)\). Therefore, \(h'\) is even.

Answer

a) \(h(-x)=\sin(f(-x))=\sin(-f(x))=-h(x)\), so \(h\) is odd. b) \(h'(x)=\cos(f(x))f'(x)\) c) Differentiating \(f(-x)=-f(x)\) gives \(-f'(-x)=-f'(x)\), so \(f'(-x)=f'(x)\). Thus, \(f'\) is even, and \(h'(-x)=\cos(-f(x))f'(x)=h'(x)\), so \(h'\) is even.
52594212
The function \(k\) is the composition of three differentiable functions: \(k(x)=f(g(h(x)))\). a) Derive a general formula for \(k'(x)\) by first viewing \(k(x)\) as \(f(V(x))\), where \(V(x)=g(h(x))\). b) Use the table to find \(k'(0)\). <table> <tr> <th>\(x\)</th> <td>\(0\)</td> <td>\(1\)</td> <td>\(2\)</td> </tr> <tr> <th>\(f(x)\)</th> <td>\(3\)</td> <td>\(0\)</td> <td>\(1\)</td> </tr> <tr> <th>\(f'(x)\)</th> <td>\(1\)</td> <td>\(-2\)</td> <td>\(6\)</td> </tr> <tr> <th>\(g(x)\)</th> <td>\(4\)</td> <td>\(0\)</td> <td>\(1\)</td> </tr> <tr> <th>\(g'(x)\)</th> <td>\(2\)</td> <td>\(3\)</td> <td>\(-1\)</td> </tr> <tr> <th>\(h(x)\)</th> <td>\(1\)</td> <td>\(2\)</td> <td>\(0\)</td> </tr> <tr> <th>\(h'(x)\)</th> <td>\(5\)</td> <td>\(4\)</td> <td>\(-3\)</td> </tr> </table>

Hints

- First treat \(g(h(x))\) as one inner function. - Apply the chain rule again when differentiating that inner function. - Evaluate the table from the inside out: begin with \(h(0)\), then evaluate \(g\), and finally evaluate the needed derivative of \(f\). - Distinguish carefully between function values and derivative values.

Solution

1. Applying the chain rule to \(k(x)=f(V(x))\) gives \(k'(x)=f'(V(x))V'(x)\). 2. Since \(V(x)=g(h(x))\), another application of the chain rule gives \(V'(x)=g'(h(x))h'(x)\). Therefore, \(k'(x)=f'(g(h(x)))g'(h(x))h'(x)\). 3. At \(x=0\), the table gives \(h(0)=1\) and \(h'(0)=5\). 4. Then \(g(h(0))=g(1)=0\), and the table gives \(g'(1)=3\) and \(f'(0)=1\). 5. Thus, \(k'(0)=f'(0)g'(1)h'(0)=1\cdot 3\cdot 5=15\).

Answer

a) \(k'(x)=f'(g(h(x)))g'(h(x))h'(x)\) b) \(k'(0)=15\)
52751412
The graph of \(h(x)=a\sqrt{x-c}\) passes through \(Q=(5,4)\) and has slope \(1\) there. a) Find \(a\) and \(c\). b) Describe how the graph of \(h\) is obtained from \(f(x)=\sqrt{x}\).

Hints

- Substitute the given point into the function to form one equation. - Use the derivative and the given slope to form a second equation. - Solve the two equations for \(a\) and \(c\). - The expression \(x-c\) controls the horizontal shift, and \(a\) controls vertical scaling.

Solution

1. The point condition gives \(a\sqrt{5-c}=4\). 2. Since \(h'(x)=\frac{a}{2\sqrt{x-c}}\), the slope condition gives \(\frac{a}{2\sqrt{5-c}}=1\), or \(a=2\sqrt{5-c}\). 3. Substitute into the point condition: \(2(5-c)=4\). Thus, \(c=3\), and then \(a=2\sqrt{2}\). 4. The graph is shifted \(3\) units right and vertically stretched by a factor of \(2\sqrt{2}\).

Answer

a) \(a=2\sqrt{2}\); \(c=3\) b) Shift right \(3\) units and vertically stretch by a factor of \(2\sqrt{2}\).
52753212
Let \(g(x)=\sqrt{12x-x^2}\). a) Find the largest real domain \(D_g\) and the equation of the normal line \(n\) to the graph of \(g\) at \(x_1=2\). b) Show algebraically that every normal line to the graph of \(g\), including those at the endpoints, passes through \(M=(6,0)\). c) Find the point \(P\) on the graph of \(g\), with \(x<6\), where the tangent line is parallel to \(y=x\).

Hints

- A normal slope is the negative reciprocal of the tangent slope when both are finite and nonzero. - Write a general normal equation at \(x_0\), and test whether \(M\) satisfies it. - Treat horizontal, vertical, and endpoint tangents as separate cases. - A tangent parallel to \(y=x\) has slope \(1\). - Check solutions in the original radical equation after squaring.

Solution

1. a) Require \(x(12-x)\ge0\), so \(D_g=[0,12]\). For \(0<x<12\), \(g'(x)=\frac{6-x}{\sqrt{12x-x^2}}\). 2. At \(x=2\), \(g(2)=2\sqrt{5}\), and the tangent slope is \(\frac{2}{\sqrt{5}}\). The normal slope is \(-\frac{\sqrt{5}}{2}\), so \(n:y=-\frac{\sqrt{5}}{2}x+3\sqrt{5}\). 3. b) For \(0<x_0<12\) and \(x_0\ne6\), the normal slope is \(m_n=\frac{\sqrt{12x_0-x_0^2}}{x_0-6}\). Substituting \(M=(6,0)\) into the normal equation gives \(0=m_n(6-x_0)+g(x_0)\), which is true. 4. At \(x_0=6\), the tangent is horizontal, so the normal is \(x=6\), which contains \(M\). At the endpoints \((0,0)\) and \((12,0)\), the tangents are vertical, so the normal is the x-axis, which also contains \(M\). 5. c) Parallelism to \(y=x\) requires \(g'(x)=1\). Thus, \(6-x=\sqrt{12x-x^2}\). Squaring gives \(x^2-12x+18=0\), with candidates \(x=6\pm3\sqrt{2}\). 6. The original unsquared equation requires \(x<6\), so \(x=6-3\sqrt{2}\). Then \(g(x)=3\sqrt{2}\), giving \(P=(6-3\sqrt{2},3\sqrt{2})\).

Answer

a) \(D_g=[0,12]\); \(n:y=-\frac{\sqrt{5}}{2}x+3\sqrt{5}\) b) Every normal contains \(M=(6,0)\); the interior, center, and endpoint cases all satisfy the claim. c) \(P=(6-3\sqrt{2},3\sqrt{2})\)
52753512
Let \(f(x)=\sqrt{8x}\) for \(x>0\). a) Find the general equation of the tangent line \(t\) to the graph of \(f\) at an arbitrary input \(x_0>0\). b) Show algebraically that this tangent line always intersects the y-axis at \(Q=\left(0,\frac{1}{2}f(x_0)\right)\). c) Suppose the graph is already drawn. Describe a straightedge-and-compass construction of the tangent line at \(P=(x_0,f(x_0))\) using the result from part b.

Hints

- Use the point-slope form of a tangent line at \(x_0\). - Differentiate the square-root function with the chain rule. - Set \(x=0\) to find a y-intercept. - Two points determine a unique line.

Solution

1. Differentiate: \(f'(x)=\frac{4}{\sqrt{8x}}\). 2. a) The tangent line is \(t(x)=\frac{4}{\sqrt{8x_0}}(x-x_0)+\sqrt{8x_0}\), which simplifies to \(t(x)=\frac{4}{\sqrt{8x_0}}x+\frac{1}{2}\sqrt{8x_0}\). 3. b) Setting \(x=0\) gives \(t(0)=\frac{1}{2}\sqrt{8x_0}=\frac{1}{2}f(x_0)\), so the y-intercept is \(Q\). 4. c) Project \(P\) horizontally to the y-axis to locate \((0,f(x_0))\). Construct the midpoint of the segment from the origin to that point; this midpoint is \(Q\). Draw the line through \(P\) and \(Q\).

Answer

a) \(t(x)=\frac{4}{\sqrt{8x_0}}x+\frac{1}{2}\sqrt{8x_0}\) b) \(t(0)=\frac{1}{2}f(x_0)\) c) Locate the point at half the height of \(P\) on the y-axis, then draw the line through that point and \(P\).
52763912
Let \(f(x)=(\ln x)^x\), where \(x>1\). a) Rewrite \(f\) in the form \(e^{g(x)}\). b) Find \(f'(x)\).

Hints

- Rewrite a variable base and exponent using the exponential function. - Differentiate the exponent using the product and chain rules. - Apply the chain rule to the outer exponential function.

Solution

1. Use \(a^b=e^{b\ln a}\): \(f(x)=e^{x\ln(\ln x)}\). Thus, \(g(x)=x\ln(\ln x)\). 2. Differentiate \(g\) using the product and chain rules: \(g'(x)=\ln(\ln x)+\frac{1}{\ln x}\). 3. Differentiate \(f(x)=e^{g(x)}\): \(f'(x)=e^{g(x)}g'(x)\). Therefore, \(f'(x)=(\ln x)^x\left(\ln(\ln x)+\frac{1}{\ln x}\right)\).

Answer

a) \(f(x)=e^{x\ln(\ln x)}\) b) \(f'(x)=(\ln x)^x\left(\ln(\ln x)+\frac{1}{\ln x}\right)\)
52936612
In optimization, a positive objective function is sometimes transformed to simplify the calculations. Suppose \(f(x)>0\) for every \(x\), and define \(h(x)=\ln(f(x))\). 1) Use the chain rule to show that every value \(x_0\) satisfying \(f'(x_0)=0\) is also a critical point of \(h\). 2) In general, what property must an outer function \(T\) have so that \(f\) has a local maximum at \(x_0\) if and only if \(g(x)=T(f(x))\) has a local maximum there? Discuss the transformations \(T(y)=y^2\) and \(T(y)=\ln(y)\).

Hints

- Apply the chain rule to the logarithm of a function. - Think about how a strictly increasing function affects the order of two input values. - Determine whether the outer function reverses or preserves inequalities. - Relate the sign of the outer derivative to the derivative of the composition.

Solution

1. By the chain rule, \(h'(x)=\frac{f'(x)}{f(x)}\). If \(f'(x_0)=0\), then \(h'(x_0)=\frac{0}{f(x_0)}=0\) because \(f(x_0)>0\). Thus, \(x_0\) is a critical point of \(h\). 2. The function \(T\) must be strictly increasing on the range of values under consideration. A strictly increasing transformation preserves the order of function values, so it preserves both the location and type of local extrema. The function \(T(y)=y^2\) is strictly increasing for \(y>0\), so it preserves local maxima of a positive function. The function \(T(y)=\ln(y)\) is strictly increasing on \((0, \infty)\), so it also preserves local maxima of a positive function.

Answer

1) Since \(h'(x)=\frac{f'(x)}{f(x)}\) and \(f(x)>0\), \(f'(x_0)=0\) implies \(h'(x_0)=0\). 2) \(T\) must be strictly increasing on the relevant range. Both \(T(y)=y^2\) for \(y>0\) and \(T(y)=\ln(y)\) for \(y>0\) have this property, so they preserve local maxima of positive functions.
53445412
The figure shows the graphs of \(u(x)=\frac{1}{2}(x^3-3x)\) and \(v(x)=2-x^2\). Define \(g(x)=u(v(x))\). a) Use the graphs to find \(g(1)\) and \(g'(1)\). b) The derivative \(g'\) has five zeros in the displayed interval. Use the graphs and the chain rule to find them.
Figure for problem 534454

Hints

- Apply the chain rule to the composition. - A product is zero when at least one factor is zero. - Identify horizontal tangents on both graphs. - Find where \(v\) takes the input values at which \(u\) has horizontal tangents, using its equation for exact values.

Solution

1. The graph gives \(v(1)=1\) and \(u(1)=-1\), so \(g(1)=-1\). 2. By the chain rule, \(g'(x)=u'(v(x))v'(x)\). Since \(u\) has a horizontal tangent at input \(1\), \(u'(1)=0\). Therefore, \(g'(1)=0\). 3. The product \(u'(v(x))v'(x)\) is zero when either factor is zero. The graph of \(v\) has a horizontal tangent at \(x=0\), giving one zero. 4. The graph of \(u\) has horizontal tangents at inputs \(-1\) and \(1\). Solve \(v(x)=1\) and \(v(x)=-1\) using \(v(x)=2-x^2\). These give \(x=\pm1\) and \(x=\pm\sqrt{3}\), respectively. 5. Thus the five zeros are \(-\sqrt{3}\), \(-1\), \(0\), \(1\), and \(\sqrt{3}\).

Answer

a) \(g(1)=-1\) and \(g'(1)=0\) b) \(x\in\{-\sqrt{3}, -1, 0, 1, \sqrt{3}\}\)

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