Calculus 2 : Derivative Review

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #3 : Derivative Defined As Limit Of Difference Quotient

What is the equation of the line tangent to the graph of the function 

\displaystyle f(x) = x^{3} + x - 17

at the point \displaystyle (3, 13) ?

Possible Answers:

\displaystyle y = 28 x- 71

\displaystyle y = 11x -20

\displaystyle y = 26 x- 65

\displaystyle y = 27 x- 68

\displaystyle y = 10x -17

Correct answer:

\displaystyle y = 28 x- 71

Explanation:

The slope of the line tangent to the graph of \displaystyle f(x) = x^{3} + x - 17 at the point \displaystyle (3, 13) is \displaystyle f'(3), which can be evaluated as follows:

\displaystyle f(x) = x^{3} + x - 17

\displaystyle f'(x) = \frac{\mathrm{d} }{\mathrm{d} x}\left ( x^{3} + x - 17 \right )

\displaystyle f'(x) = 3x^{2} + 1

\displaystyle f'(3) = 3\cdot 3^{2} + 1 = 28

The line with slope 28 through \displaystyle (3, 13) has equation:

\displaystyle y - y_{1} = m (x-x_{1})

\displaystyle y -13= 28 (x-3)

\displaystyle y -13= 28 x- 28 \cdot 3

\displaystyle y -13= 28 x- 84

\displaystyle y = 28 x- 71

Example Question #71 : Derivative Review

Let the initial approximation of the ninth root of 100 be 

\displaystyle x_{1}= 2.

Use one iteration of Newton's method to find approximation \displaystyle x_{2}. Give your answer to the nearest thousandth.

Possible Answers:

\displaystyle 1.971

\displaystyle 2.021

\displaystyle 1.871

\displaystyle 1.821

\displaystyle 1.921

Correct answer:

\displaystyle 1.821

Explanation:

This is equivalent to finding a solution of the equation 

\displaystyle x^9 = 100

or the zero of the polynomial

\displaystyle P (x) = x^9 - 100

Using Newton's method, we can find \displaystyle x_{2} from the formula

\displaystyle x_{2} = x_{1} - \frac{P(x_{1})}{P'(x_{1})}.

\displaystyle P '(x) = 9 x^8, so 

\displaystyle P (x_{1}) = P(2)= 2^9 - 100 = 512 - 100 = 412

\displaystyle P '(x_{1}) = P' (2)= 9 \cdot 2^8 = 9 \cdot 256 = 2,304

\displaystyle x_{2} = 2 - \frac{P(2)}{P'(2)} = 2 - \frac{412}{2,304} \approx 2 - 0.1788 \approx 1.821

Example Question #2 : Chain Rule And Implicit Differentiation

\displaystyle g(x) = e ^{x^{2}+x}

Evaluate \displaystyle g '(3 ).

Possible Answers:

\displaystyle 7 e^{9}

\displaystyle e^{7}

\displaystyle 12 e^{11}

\displaystyle 12 e^{12}

\displaystyle 7 e^{12}

Correct answer:

\displaystyle 7 e^{12}

Explanation:

To find \displaystyle g'(x), substitute \displaystyle u = x ^{2} + x and use the chain rule:

\displaystyle g(x) = e ^{x^{2}+x}

\displaystyle g'(x) = \frac{\mathrm{d} }{\mathrm{d} x} e ^{x^{2}+x}

\displaystyle = \frac{\mathrm{d} }{\mathrm{d} x} e ^{u}

\displaystyle = \frac{\mathrm{d}u }{\mathrm{d} x} \cdot \frac{\mathrm{d} }{\mathrm{d} u}e ^{u}

\displaystyle = \frac{\mathrm{d}u }{\mathrm{d} x} \cdot e ^{u}

\displaystyle = \frac{\mathrm{d} }{\mathrm{d} x}\left ( x ^{2} + x \right ) \cdot \frac{\mathrm{d} }{\mathrm{d} u}e ^{u}

\displaystyle = \left ( 2x + 1 \right ) \cdot e ^{u}

\displaystyle = \left ( 2x + 1 \right ) \cdot e ^{ x ^{2} + x}

 

\displaystyle g'(x)= \left ( 2x + 1 \right ) e ^{ x ^{2} + x}

Plug in 3:

\displaystyle g'(3)= \left ( 2 \cdot 3 + 1 \right ) \cdot e ^{ 3 ^{2} + 3}

\displaystyle = \left ( 6 + 1 \right ) \cdot e ^{ 9+ 3} =7e ^{ 12}

Example Question #3 : Chain Rule And Implicit Differentiation

\displaystyle g (x) = \frac{1}{4x - 7}

Evaluate \displaystyle g ' (1 ).

Possible Answers:

\displaystyle \frac{4}{9}

Undefined

\displaystyle \frac{4}{3}

\displaystyle -\frac{4}{3}

\displaystyle - \frac{4}{9}

Correct answer:

\displaystyle - \frac{4}{9}

Explanation:

To find \displaystyle g'(x), substitute \displaystyle u =4x - 7 and use the chain rule: 

\displaystyle g (x) = \frac{1}{4x - 7}

\displaystyle g '(x) = \frac{\mathrm{d} }{\mathrm{d} x}\cdot \frac{1}{4x - 7}

\displaystyle = \frac{\mathrm{d} }{\mathrm{d} x}\cdot \frac{1}{u}

\displaystyle = \frac{\mathrm{d} u}{\mathrm{d} x}\cdot \frac{\mathrm{d} }{\mathrm{d} u} \frac{1}{u}

\displaystyle = \frac{\mathrm{d} }{\mathrm{d} x} (4x-7) \cdot \frac{\mathrm{d} }{\mathrm{d} u} u ^{-1}

\displaystyle =4 \cdot (-1 ) u ^{-1-1}

\displaystyle =-4 u ^{-2} = - \frac{4}{u^{2}}= - \frac{4}{(4x-7)^{2}}

So

\displaystyle g'(x)= - \frac{4}{(4x-7)^{2}}

and

\displaystyle g'(1)= - \frac{4}{(4 \cdot 1 -7)^{2}}

\displaystyle = - \frac{4}{(4 -7)^{2}}

\displaystyle = - \frac{4}{(-3)^{2}} = - \frac{4}{9}

Example Question #71 : Derivatives

\displaystyle g (x) = \tan \left ( x +\frac{ \pi }{4}\right )

Evaluate .

Possible Answers:

\displaystyle 2

Undefined

\displaystyle -\sqrt{2}

\displaystyle \sqrt{2}

\displaystyle -2

Correct answer:

\displaystyle 2

Explanation:

To find \displaystyle g'(x), substitute \displaystyle u = x +\frac{ \pi }{4} and use the chain rule:

\displaystyle g (x) = \tan \left ( x +\frac{ \pi }{4}\right )

\displaystyle g' (x) = \frac{\mathrm{d} }{\mathrm{d} x}\tan \left ( x +\frac{ \pi }{4}\right )

\displaystyle g' (x) = \frac{\mathrm{d} }{\mathrm{d} x}\tan u

\displaystyle =\frac{\mathrm{d} u}{\mathrm{d} x} \cdot \frac{\mathrm{d} }{\mathrm{d} u} \tan u

\displaystyle =\frac{\mathrm{d} }{\mathrm{d} x} \left ( x +\frac{ \pi }{4} \right )\cdot \frac{\mathrm{d} }{\mathrm{d} u} \tan u

\displaystyle =\frac{\mathrm{d} }{\mathrm{d} x} \left ( x +\frac{ \pi }{4} \right ) \cdot \sec ^{2} u

\displaystyle =1 \cdot \sec ^{2}\left ( x +\frac{ \pi }{4}\right ) = \sec ^{2}\left ( x +\frac{ \pi }{4}\right )

 

 \displaystyle g'(x) = \sec ^{2}\left ( x +\frac{ \pi }{4}\right )

\displaystyle g'(\pi ) = \sec ^{2}\left ( \pi +\frac{ \pi }{4}\right )

\displaystyle g'(\pi ) = \sec ^{2}\frac{ 5 \pi }{4}

\displaystyle = \left ( - \sqrt{2 }\right )^{2} = 2

Example Question #4 : Chain Rule And Implicit Differentiation

\displaystyle g (x) = 3 ^{x^{2}}

Evaluate \displaystyle g ' (-1 ).

Possible Answers:

\displaystyle -2

\displaystyle 0

\displaystyle -\frac{3 \ln 3}{2}

\displaystyle -6 \ln 3

\displaystyle 9

Correct answer:

\displaystyle -6 \ln 3

Explanation:

To find \displaystyle g'(x), substitute \displaystyle u = x ^{2} and use the chain rule: 

\displaystyle g (x) = 3 ^{x^{2}}

\displaystyle g ' (x) = \frac{\mathrm{d} }{\mathrm{d} x} 3 ^{x^{2}}

\displaystyle = \frac{\mathrm{d} }{\mathrm{d} x} 3 ^{u}

\displaystyle = \frac{\mathrm{d}u }{\mathrm{d} x} \cdot \frac{\mathrm{d} }{\mathrm{d} u} 3 ^{u}

\displaystyle = \frac{\mathrm{d}}{\mathrm{d} x} x^{2} \cdot \frac{\mathrm{d} }{\mathrm{d} u} 3 ^{u}

\displaystyle = 2x \cdot \ln 3 \cdot 3 ^{u}

\displaystyle = 2x \ln 3 \cdot 3 ^{x^2}

So \displaystyle g'(x)= 2x \ln 3 \cdot 3 ^{x^2}

and

\displaystyle g'(-1)= 2(-1) \ln 3 \cdot 3 ^{(-1)^2}

\displaystyle = -2 \ln 3 \cdot 3 ^{1} = -2 \ln 3 \cdot 3 = -6 \ln 3

Example Question #72 : Derivatives

\displaystyle g \left (x \right )= \cos \left ( \pi x^{2}\right )

Evaluate \displaystyle g ' \left ( \frac{1}{2} \right ).

Possible Answers:

\displaystyle \pi \sqrt{2}

\displaystyle - \pi \sqrt{2}

\displaystyle - \frac{ \sqrt{2}}{2 \pi}

\displaystyle - \frac{ \pi \sqrt{2}}{2}

\displaystyle \frac{ \pi \sqrt{2}}{2}

Correct answer:

\displaystyle - \frac{ \pi \sqrt{2}}{2}

Explanation:

To find \displaystyle g'(x), substitute \displaystyle u = \pi x^{2} and use the chain rule:

\displaystyle g \left (x \right )= \cos \left ( \pi x^{2}\right )

\displaystyle g'(x)= \frac{\mathrm{d} }{\mathrm{d} x} \cos \left ( \pi x^{2}\right )

\displaystyle = \frac{\mathrm{d} }{\mathrm{d} x} \cos u

\displaystyle =\frac{\mathrm{d} u}{\mathrm{d} x} \cdot \frac{\mathrm{d} }{\mathrm{d} u} \cos u

\displaystyle =\frac{\mathrm{d} }{\mathrm{d} x} \pi x^{2} \cdot \frac{\mathrm{d} }{\mathrm{d} u} \cos u

\displaystyle = \pi \cdot 2 x\cdot \left ( - \sin u \right )

So 

and 

\displaystyle g ' \left ( \frac{1}{2} \right )=-2 \pi\cdot \frac{1}{2} \sin \left [\pi \cdot \left ( \frac{1}{2} \right )^{2} \right ]

\displaystyle =- \pi \sin \left ( \frac{\pi}{4} \right )

\displaystyle =- \pi \cdot \frac{\sqrt{2}}{2} = - \frac{ \pi \sqrt{2}}{2}

Example Question #74 : Derivative Review

What is the equation of the line tangent to the graph of the function 

\displaystyle f(x)= x^3-2

at \displaystyle (2,6) ?

Possible Answers:

\displaystyle y = 10 x-14

\displaystyle y = 12 x+18

\displaystyle y = 24 x-42

\displaystyle y = 12 x-18

\displaystyle y = 10 x+14

Correct answer:

\displaystyle y = 12 x-18

Explanation:

The slope of the line tangent to the graph of \displaystyle f(x)= x^3-2 at \displaystyle (2,6) is

\displaystyle f'(2), which can be evaluated as follows:

\displaystyle f(x)= x^3-2

\displaystyle f'(x)= 3x^{3-1}-0

\displaystyle f'(x)= 3x^{2}

Then \displaystyle f'(2)= 3 \cdot 2^{2} = 3 \cdot4 = 12, which is the slope of the line.

The equation of the line with slope 12 through \displaystyle (2,6) is:

\displaystyle y - y_{1} = m (x-x_{1})

\displaystyle y - 6 = 12 (x-2)

\displaystyle y - 6 = 12 x-24

\displaystyle y - 6 + 6= 12 x-24 + 6

\displaystyle y = 12 x-18

Example Question #71 : Derivative Review

Let the initial approximation of the seventh root of 1,000 be 

\displaystyle x_{1}= 3.

Use one iteration of Newton's method to find approximation \displaystyle x_{2}. Give your answer to the nearest thousandth.

Possible Answers:

\displaystyle 2.787

\displaystyle 2.707

\displaystyle 2.767

\displaystyle 2.727

\displaystyle 2.687

Correct answer:

\displaystyle 2.767

Explanation:

This is equivalent to finding a solution of the equation 

\displaystyle x^7 = 1,000

or the zero of the polynomial

\displaystyle P (x) = x^7 - 1,000

Using Newton's method, we can find \displaystyle x_{2} from the formula

\displaystyle x_{2} = x_{1} - \frac{P(x_{1})}{P'(x_{1})}.

\displaystyle P'(x) = 7x^6, so

\displaystyle P (x_{1}) =P(3)= 3^7 - 1,000 = 2,187 - 1,000 = 1,187

\displaystyle P'(x_{1}) = P'(3)= 7 \cdot 3^6 = 7 \cdot 729 = 5,103

\displaystyle x_{2} = 3 - \frac{P(3)}{P'(3)} = 3 - \frac{1,187}{5,103} \approx 3 - 0.2326 \approx 2.767

Example Question #72 : Derivatives

Let the initial approximation of a solution of the equation

\displaystyle x^3 = x + 19

be \displaystyle x_{1} = 2.5.

Use one iteration of Newton's method to find an approximation of \displaystyle x_{2}. Give your answer to the nearest thousandth.

Possible Answers:

\displaystyle 2.781

\displaystyle 2.731

\displaystyle 2.681

\displaystyle 2.831

\displaystyle 2.881

Correct answer:

\displaystyle 2.831

Explanation:

Rewrite the equation to be solved for \displaystyle x as 

\displaystyle x^3 - x - 19 = 0.

Let \displaystyle f(x) = x^3 - x - 19.  

Then,

\displaystyle f'(x) = \frac{\mathrm{d} }{\mathrm{d} x} \left ( x^3 - x - 19 \right ).

\displaystyle f'(x) =3x^2 - 1

The problem amounts to finding a zero of \displaystyle f(x ). By Newton's method, the second approximation can be derived from the first using the equation

\displaystyle x_{2} = x_{1} - \frac{f(x_{1})}{f'(x_{1})}.

\displaystyle x_{1} = 2.5, so

\displaystyle f(2.5) = 2.5^3 - 2.5 - 19 = 15.625 - 2.5 - 19 = -5.875

and 

\displaystyle f'(2.5) =3 \cdot 2.5^2 - 1 = 3 \cdot 6.25 - 1 = 18.75 - 1 = 17.75

\displaystyle x_{2} = 2.5 - \frac{f(2.5)}{f'(2.5)}= 2.5 - \frac{ -5.875}{17.75}\approx 2.5 - (-0.3310) \approx 2.831

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