Calculus 2 : Derivative Review

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #42 : Derivative At A Point

What is the slope of a function \displaystyle f(x)=3x^{2}+7x-5 at \displaystyle (2,6)?

Possible Answers:

\displaystyle -19

\displaystyle 12

\displaystyle 19

\displaystyle -12

\displaystyle 7

Correct answer:

\displaystyle 19

Explanation:

We define slope as the first derivative of a given function.

Since we have

\displaystyle f(x)=3x^{2}+7x-5, we can use the Power Rule  

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1}for all \displaystyle n\neq0 to determine that

\displaystyle f'(x)=(2)3x^{2-1}+(1)7x^{1-1}-(0)5=6x+7 .

We also have a point \displaystyle (2,6) with a \displaystyle x-coordinate \displaystyle 2, so the slope

\displaystyle f'(2)=6(2)+7=12+7=19.

Example Question #43 : Derivative At A Point

What is the slope of a function \displaystyle f(x)=5x^{2}-9x+14 at \displaystyle (-4,2)?

Possible Answers:

\displaystyle -49

\displaystyle 14

\displaystyle -14

\displaystyle 49

\displaystyle -40

Correct answer:

\displaystyle -49

Explanation:

We define slope as the first derivative of a given function.

Since we have 

\displaystyle f(x)=5x^{2}-9x+14, we can use the Power Rule  

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1}for all \displaystyle n\neq0 to determine that 

\displaystyle f'(x)=(2)5x^{2-1}-(1)9x^{1-1}+(0)14=10x-9 .

We also have a point \displaystyle (-4,2) with a \displaystyle x-coordinate \displaystyle -4, so the slope

\displaystyle f'(-4)=10(-4)-9=-40-9=-49.

Example Question #131 : Derivative Review

What is the slope of a function \displaystyle f(x)=2x^{2}+13x-7 at \displaystyle (-1,1)?

Possible Answers:

\displaystyle -5

\displaystyle 9

\displaystyle 13

\displaystyle -8

\displaystyle 8

Correct answer:

\displaystyle 9

Explanation:

We define slope as the first derivative of a given function.

Since we have 

\displaystyle f(x)=2x^{2}+13x-7, we can use the Power Rule

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1}for all \displaystyle n\neq0 to determine that 

\displaystyle f'(x)=(2)2x^{2-1}+(1)13x^{1-1}-(0)7=4x+13 .

We also have a point \displaystyle (-1,1) with a \displaystyle x-coordinate \displaystyle -1, so the slope

\displaystyle f'(-1)=4(-1)+13=-4+13=9.

Example Question #51 : Derivative At A Point

Find \displaystyle f'(0) for

\displaystyle f(x)=x^3\ln(x+1)

Possible Answers:

\displaystyle 3

\displaystyle 1

\displaystyle \infty

\displaystyle 0

\displaystyle 2

Correct answer:

\displaystyle 0

Explanation:

In order to find the derivative, we need to find \displaystyle f'(x). We can find this by remembering the product rule and knowing the derivative of natural log.

Product Rule:

\displaystyle [f(x)g(x)]'=f'(x)g(x)+f(x)g'(x).

 

Derivative of natural log:

\displaystyle f(x)=\ln(g(x))

\displaystyle f'(x)=\frac{g'(x)}{g(x)}

Now lets apply this to our problem.

\displaystyle f(x)=x^3\ln(x+1)

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

\displaystyle f'(0)=3(0)^2\ln(0+1)+\frac{0^3}{0+1}=0

Example Question #131 : Derivative Review

Find the derivative of the following function at the point \displaystyle z=0:
\displaystyle f(z)=\frac{z^2\cos(z)}{2}

 

Possible Answers:

\displaystyle 0

\displaystyle -4

\displaystyle 4

\displaystyle 1

Correct answer:

\displaystyle 0

Explanation:

The derivative of the function is

\displaystyle f'(z)=\frac{4z\cos(z)-2z^2\sin(z)}{4}

which was found using the following rules:

\displaystyle \frac{d}{dx}\left[\frac{f(x)}{g(x)}\right]=\frac{g(x)f'(x)-f(x)g'(x)}{(g(x))^2},

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

\displaystyle \frac{d}{dx}(x^n)=nx^{n-1}

Finally, plug in the point \displaystyle z=0 into the first derivative function:

\displaystyle f'(0)=\frac{0}{4}=0

 

Example Question #132 : Derivative Review

Find the derivative of the following function at \displaystyle \theta=2\pi:

\displaystyle f(\theta )=\sin^3(\theta)+e^{\theta}

Possible Answers:

\displaystyle e^{2\pi}

\displaystyle 1

\displaystyle 3+2\pi e^{2\pi}

\displaystyle 0

Correct answer:

\displaystyle e^{2\pi}

Explanation:

The derivative of the function is

\displaystyle f'(\theta)=3\sin^2(\theta)\cos(\theta)+ e^{\theta}

and was found using the following rules:

\displaystyle \frac{d}{dx}(e^{u})=e^{u}\frac{du}{dx},

 \displaystyle \frac{d}{dx}f(g(x))=f'(g(x))\cdot g'(x)

\displaystyle \frac{d}{dx}\sin(x)=\cos(x),

\displaystyle \frac{d}{dx}(x^n)=nx^{^{n-1}}

To finish the problem, plug in \displaystyle \theta=2 \pi into the derivative function:

\displaystyle f'(2 \pi)= e^{2\pi}.

Example Question #51 : Derivative At A Point

Find the derivative of the following function at \displaystyle y=2 \pi

\displaystyle f(y)=\sec^2(y)+\tan(y).

 

Possible Answers:

\displaystyle 0

\displaystyle 1

undefined

\displaystyle \infty

Correct answer:

\displaystyle 1

Explanation:

The derivative of the function is

\displaystyle f'(y)=2\sec^2(y)\tan(y)+\sec^2(y)

and was found using the following rules:

\displaystyle \frac{d}{dx}\tan(x)=\sec^2(x)\displaystyle \frac{d}{dx} \sec(x)=\sec(x)\tan(x)\displaystyle \frac{d}{dx} f(g(x))=f'(g(x))\cdot g'(x)\displaystyle \frac{d}{dx}(x^n)=nx^{n-1}

Then, plug in the point given into the first derivative function:

\displaystyle f'(2 \pi) = 2(1)(0)+1=1

Example Question #51 : Derivative At A Point

Find the second derivative of the following function at \displaystyle x=0:

\displaystyle f(x)=\cos(x)+e^\frac{x}{2}+x^3+x^2

Possible Answers:

\displaystyle 1

\displaystyle \frac{5}{4}

Correct answer:

\displaystyle \frac{5}{4}

Explanation:

We must find the first derivative of the function first:

\displaystyle f'(x)=-\sin(x)+\frac{e^{\frac{x}{2}}}{2}+3x^2+2x

The derivative was found using the following rules:

\displaystyle \frac{d}{dx}\cos(x)=-\sin(x)\displaystyle \frac{d}{dx}(e^u)=e^u\frac{du}{dx}\displaystyle \frac{d}{dx}(x^n)=nx^{n-1}

Find the second derivative of the function by taking the derivative of the above function:

\displaystyle f''(x)=-\cos(x)+\frac{e^{\frac{x}{2}}}{4}+6x+2

An additional rule was used:

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

Now, plug in x=0 into the above function:

\displaystyle f''(0)=-1+\frac{1}{4}+2=\frac{5}{4}

Example Question #131 : Derivative Review

Find the second derivative of the following function at \displaystyle x=0:

\displaystyle e^{2x}+2x\cos(3x)

Possible Answers:

\displaystyle 5

\displaystyle 0

\displaystyle 6

\displaystyle 4

Correct answer:

\displaystyle 4

Explanation:

To find the second derivative of the function, we first must find the first derivative of the function:

\displaystyle f'(x)=2e^{2x}+2\cos(3x)-6x\sin(3x)

The derivative was found using the following rules:

\displaystyle \frac{d}{dx}\cos(x)=-\sin(x)\displaystyle \frac{d}{dx}e^u=e^u\frac{du}{dx}\displaystyle \frac{d}{dx}(x^n)=nx^{n-1}\displaystyle \frac{d}{dx}f(g(x))=f'(g(x))\cdot g'(x)\displaystyle \frac{d}{dx}f(x)g(x)=f'(x)g(x)+f(x)g'(x)

The second derivative is simply the derivative of the first derivative function, and is equal to:

\displaystyle f''(x)=4e^{2x}-12\sin(3x)-18x\cos(3x)

One more rule used in combination with some of the ones above is:

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

To finish the problem, plug in x=0 into the above function to get an answer of \displaystyle 4.

Example Question #52 : Derivative At A Point

What is the slope of \displaystyle f(x)=9x^{2}-12x+5 at \displaystyle (4,-4)?

Possible Answers:

\displaystyle 12

\displaystyle -60

\displaystyle 60

\displaystyle 30

\displaystyle -12

Correct answer:

\displaystyle 60

Explanation:

We define slope as the first derivative of a given function.

Since we have

\displaystyle f(x)=9x^{2}-12x+5, we can use the Power Rule

\displaystyle \frac{d}{dx}x^{n}=nx^{n-1} for all \displaystyle n\neq0 to determine that

\displaystyle f'(x)=(2)9x^{2-1}-(1)12x+(0)5=18x-12 .

We also have a point \displaystyle (4,-4) with a \displaystyle x-coordinate \displaystyle 4, so the slope

\displaystyle f'(4)=18(4)-12=72-12=60 .

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