AP Calculus AB : Computation of the Derivative

Study concepts, example questions & explanations for AP Calculus AB

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Example Questions

Example Question #291 : Computation Of The Derivative

Find the derivative of \displaystyle 15x^5-2x^4+11x^2+e^x-\ln x.

Possible Answers:

\displaystyle 15x^4-2x^3+11x+e^x-\ln x

\displaystyle 55x^4-6x^3+22x

\displaystyle 25x^4+2x^3+11x+e^x+\ln x

Correct answer:

Explanation:

Take the derivative of each term.

Add them:

Example Question #292 : Computation Of The Derivative

Find the derivative of \displaystyle 2\sin x\cos x.

Possible Answers:

\displaystyle 2\cos2x

\displaystyle 2

\displaystyle -\sin^2x+cos^2x

\displaystyle -2\cos x\sin x

\displaystyle 2\sin2x

Correct answer:

\displaystyle 2\cos2x

Explanation:

There are two ways to solve this problem.

First, you can use a trig identity to replace \displaystyle 2\sin x\cos x with \displaystyle \sin 2x. Using the chain rule, \displaystyle (\sin 2x)'=2\cos2x.

Alternatively, you could use the product rule.

\displaystyle 2(\sin x(-\sin x)+\cos x(\cos x))=2(\cos^2x-\sin^2x)

Since \displaystyle \cos^2x-\sin^2x=\cos2x, our final answer is still \displaystyle 2\cos2x.

Example Question #293 : Computation Of The Derivative

Find the derivative of \displaystyle \frac{e^x}{\sin x}.

Possible Answers:

\displaystyle \frac{-e^x\tan x}{\sin x}

\displaystyle \frac{e^x\sin x-e^x\cos x}{\sin x}

\displaystyle \frac{e^x-e^x\tan x}{\sin x}

\displaystyle \frac{e^x\tan x-e^x}{\cos x}

\displaystyle \frac{e^x}{\cos x}

Correct answer:

\displaystyle \frac{e^x-e^x\tan x}{\sin x}

Explanation:

For this problem, we need to use the quotient rule.

\displaystyle (\frac{f}{g})'=\frac{gf'-fg'}{g^2}

\displaystyle (\frac{e^x}{\sin x})'=\frac{\sin x(e^x)-e^x(\cos x)}{\sin^2x}

Simplifying:

\displaystyle e^x (\frac{\sin x-\cos x}{\sin^2x})=\frac{e^x-e^x\tan x}{\sin x}

Example Question #461 : Derivatives

Find the derivative of \displaystyle y=(2x^4+5x)(cos(x))

Possible Answers:

\displaystyle y'=8x^3cos(x)+5cos(x)

\displaystyle y'=-2x^4sin(x)+8x^3cos(x)-5xsin(x)+5cos(x)

\displaystyle y'=2x^4cos(x)-2x^4sin(x)+5xcos(x)-5xsin(x)

None of the other answers

Correct answer:

\displaystyle y'=-2x^4sin(x)+8x^3cos(x)-5xsin(x)+5cos(x)

Explanation:

\displaystyle \frac{d}{dx}[2x^4+5x]=8x^3+5

 

\displaystyle \frac{d}{dx}[cos(x)]=-sin(x)

 

 

Product rule states: \displaystyle \frac{d}{du}[f(u) \cdot g(u)]=f'(u)g(u)+g'(u)f(u)

 

Therefore:

 \displaystyle y'=(8x^3+5)(cos(x))-sin(x)(2x^4+5x)

\displaystyle =-2x^4sin(x)+8x^3cos(x)-5xsin(x)+5cos(x)

Example Question #471 : Derivatives

Use the chain rule to differentiate the following function: \displaystyle h(x)=sin(x^{2}e^{x})

Possible Answers:

\displaystyle h^{'}(x)=sin(x^{2}e^{x})xe^{x}(2+x)

\displaystyle h^{'}(x)=-cos(x^{2}e^{x})xe^{x}(2+x)

\displaystyle h^{'}(x)=-sin(x^{2}e^{x})xe^{x}(2+x)

\displaystyle h^{'}(x)=cos(x^{2}e^{x})xe^{x}(2+x)

Correct answer:

\displaystyle h^{'}(x)=cos(x^{2}e^{x})xe^{x}(2+x)

Explanation:

\displaystyle h(x)=sin(x^{2}e^{x})

By the chain rule: \displaystyle h^{'}(x)=cos(x^{2}e^{x})\frac{\mathrm{d} }{\mathrm{d} x}(x^{2}e^{x})

Differentiate \displaystyle (x^{2}e^{x}) using the product rule: \displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(x^{2}e^{x})=\frac{\mathrm{d} }{\mathrm{d} x}(x^{2})e^{x}+x^{2}\frac{\mathrm{d} }{\mathrm{d} x}e^{x}=2xe^{x}+x^{2}e^{x}

Substitute this derivative for \displaystyle \frac{\mathrm{d} }{\mathrm{d} x}(x^{2}e^{x}) in the first equation: \displaystyle h^{'}(x)=cos(x^{2}e^{x})(2xe^{x}+x^{2}e^{x})

Factor the equation: \displaystyle h^{'}(x)=cos(x^{2}e^{x})xe^{x}(2+x)

 

Example Question #771 : Ap Calculus Ab

\displaystyle f(p)=cos(2p-1)-(2p^3+4p)

 

Find \displaystyle f'(p).

Possible Answers:

\displaystyle f'(p)=cos(2p-1)+sin(2p-1)-6p^2+4

\displaystyle f'(p)=-2cos(2p-1)(p^3+3p^2+2p+2)

\displaystyle f'(p)=sin(2p-1)-sin(2p^3+4p)

\displaystyle f'(p) is undefined.

\displaystyle f'(p)=-2(sin(2p-1)+3p^2+2)

Correct answer:

\displaystyle f'(p)=-2(sin(2p-1)+3p^2+2)

Explanation:

\displaystyle \frac{d}{dx}[cos(2p-1)]=2 \cdot -sin(2p-1)=-2sin(2p-1)

 

\displaystyle \frac{d}{dx}[2p^3+4p]=6p^2+4

 

Therefore:

\displaystyle f'(p)=-2sin(2p-1)-(6p^2+4)

\displaystyle =-2sin(2p-1)-6p^2-4

\displaystyle =-2(sin(2p-1)+3p^2+2)

 

 

 

\displaystyle f'(p)=-2(3p^2+sin(2p-1)+2)

Example Question #661 : Derivatives

Let \displaystyle f(x)=sin(x)-cos(x).

Find the second derivative of \displaystyle f(x).

Possible Answers:

\displaystyle f''(x)=sin^2(x)+cos^2(x)

\displaystyle f''(x)=sin^2(x)-cos^2(x)

\displaystyle f''(x)=sin(x)-cos(x)

\displaystyle f''(x)=sin(x)+cos(x)

\displaystyle f''(x)=cos(x)-sin(x)

Correct answer:

\displaystyle f''(x)=cos(x)-sin(x)

Explanation:

The second derivative is just the derivative of the first derivative. So first we find the first derivative of \displaystyle f(x). Remember the derivative of \displaystyle \sin x is \displaystyle \cos x, and the derivative for \displaystyle \cos x is \displaystyle -\sin x.

 \displaystyle f'(x)= cos(x)+sin(x)

 

Then to get the second derivative, we just derive this function again. So

\displaystyle f''(x)=-sin(x)+cos(x)=cos(x)-sin(x)

Example Question #662 : Derivatives

Define \displaystyle f (x) = 6x^{3} - 12x^{2} + 4x -8.

What is \displaystyle f ' ' (x)?

Possible Answers:

\displaystyle f ' '(x) = 36x - 24

\displaystyle f ''(x) = 18x - 24

\displaystyle f ' '(x) = 36x

\displaystyle f ' '(x) = 18

\displaystyle f ' '(x) = 6x - 1 2

Correct answer:

\displaystyle f ' '(x) = 36x - 24

Explanation:

Take the derivative \displaystyle f' of \displaystyle f, then take the derivative of \displaystyle f'.

\displaystyle f (x) = 6x^{3} - 12x^{2} + 4x -8

 

\displaystyle f '(x) = 3 \cdot 6x^{3-1} - 2 \cdot 12x^{2-1} + 4 -0

\displaystyle f '(x) = 18x^{2} - 24x+ 4

 

\displaystyle f ' '(x) = 2 \cdot 18x^{2-1} - 24+ 0

\displaystyle f ' '(x) = 36x - 24

Example Question #12 : Finding Second Derivative Of A Function

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

What is \displaystyle g''(x)?

Possible Answers:

\displaystyle g''(x) =4x^2 \cos(x^2)

\displaystyle g''(x) =-4x^2 \cos(x^2)

\displaystyle g''(x) = -4x^2 \sin(x^2)

Correct answer:

Explanation:

Take the derivative \displaystyle g' of \displaystyle g, then take the derivative of \displaystyle g'.

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

 

\displaystyle g'(x) = 2x \cdot [-\sin (x^2)]

\displaystyle g'(x) = - 2x \sin (x^2)

 

\displaystyle g''(x) = - 2\left [ 1 \cdot \sin(x^2)+ x \cdot 2x \cos(x^2) \right ]

\displaystyle g''(x) = - 2\left [ \sin(x^2)+ 2x^2 \cos(x^2) \right ]

Example Question #13 : Finding Second Derivative Of A Function

Define \displaystyle f(x) = \frac{1}{e^{4x}}.

What is \displaystyle f ''(x)?

Possible Answers:

\displaystyle f''(x) =- \frac{16 }{e^{4x}}

\displaystyle f''(x) = \frac{1 }{e^{4x-2}}

\displaystyle f(x) = \frac{1}{16e^{4x}}

\displaystyle f''(x) = \frac{1 }{e^{4x+2}}

\displaystyle f''(x) = \frac{16 }{e^{4x}}

Correct answer:

\displaystyle f''(x) = \frac{16 }{e^{4x}}

Explanation:

Rewrite:

\displaystyle f(x) = \frac{1}{e^{4x}}

\displaystyle f(x) = e^{-4x}

Take the derivative \displaystyle f' of \displaystyle f, then take the derivative of \displaystyle f'.

\displaystyle f'(x) = -4 e^{-4x}

\displaystyle f''(x) = -4 \cdot \left (-4 \right )e^{-4x} = 16e^{-4x} = \frac{16 }{e^{4x}}

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