Calculus 1 : Functions

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #691 : Functions

Differentiate \displaystyle H(x)=\int_{2}^{x} \ln (\sqrt{t^2+16}) \ dt. 

Possible Answers:

\displaystyle \ln (\sqrt{x^2+16}) - \ln (\sqrt{20})

\displaystyle \frac{x}{x^2+16}

\displaystyle \ln (\sqrt{x^2+16})

\displaystyle \ln (\sqrt{t^2+16})

Correct answer:

\displaystyle \ln (\sqrt{x^2+16})

Explanation:

By Fundamental Theorem of Calculus,

 \displaystyle \frac{dH}{dx}=\frac{\mathrm{d} }{\mathrm{d} x} \int_{2}^{x} \ln (\sqrt{t^2+16}) \ dt = H'(x) \cdot \frac{d}{dx}x = \ln(\sqrt{x^2+16}) \cdot 1 =\ln(\sqrt{x^2+16}).

Example Question #692 : Functions

Find the derivative of the function

 \displaystyle f(x) = \sin x + x^2 + \frac{5}{27} e^2.

Possible Answers:

\displaystyle - \cos x +2x + \frac{10}{27}e

\displaystyle \cos x + 2x + \frac{10}{27}e

\displaystyle - \cos x + 2x

\displaystyle \cos x + 2x

Correct answer:

\displaystyle \cos x + 2x

Explanation:

Since \displaystyle \frac{5}{27}e^2 is a constant, its derivative is \displaystyle 0. Therefore, \displaystyle f'(x) = \cos x + 2x.

Example Question #505 : How To Find Differential Functions

Find two numbers which add up to fifty such that their product is the maximum value possible.

Possible Answers:

\displaystyle 0,50

\displaystyle 20,30

\displaystyle 15,35

\displaystyle 25,25

\displaystyle 5,45

Correct answer:

\displaystyle 25,25

Explanation:

To begin with write the information of the problem in mathematical terms. We're told the sum of two numbers is fifty:

\displaystyle x+y=50

Their product is then:

\displaystyle f(x,y)=xy

We're uncertain currently about what these two numbers are, but we can relate them:

\displaystyle y=50-x

So that we can simplify the product function:

\displaystyle f(x)=x(50-x)

\displaystyle f(x)=50x-x^2

Maxima and minima occur where the derivative of a function is zero. Take the derivative of this function:

\displaystyle f'(x)=50-2x

And set it to zero:

\displaystyle 50-2x=0

\displaystyle -2x=-50

\displaystyle x=25

\displaystyle y=50-x=50-25=25

You can validate that this is a minimum due to the derivative function having positive values before this point, and negative values after this point.

Example Question #507 : How To Find Differential Functions

Let \displaystyle f(x)=(x^2+1)^5 on the interval \displaystyle (0,2). Find a value for the number(s) that satisfies the mean value theorem for this function and interval.

Possible Answers:

\displaystyle 0.299

\displaystyle 0.753

\displaystyle 1.119

\displaystyle 1.484

\displaystyle 1.986

Correct answer:

\displaystyle 1.484

Explanation:

The mean value theorem states that for a planar arc passing through a starting and endpoint \displaystyle (a,b);a< b, there exists at a minimum one point, \displaystyle c, within the interval \displaystyle (a,b) for which a line tangent to the curve at this point is parallel to the secant passing through the starting and end points.

Meanvaluetheorem

In other words, if one were to draw a straight line through these start and end points, one could find a point on the curve where the tangent would have the same slope as this line.

\displaystyle f'(c)=\frac{f(b)-f(a)}{b-a}=\frac{Rise}{Run};a< c< b

Note that the value of the derivative of a function at a point is the function's slope at that point; i.e. the slope of the tangent at said point.

First, find the two function values of

\displaystyle f(x)=(x^2+1)^5 on the interval \displaystyle (0,2)

\displaystyle f(0)=(0^2+1)^5=1

\displaystyle f(2)=(2^2+1)^5=3125

Then take the difference of the two and divide by the interval.

\displaystyle \frac{3125-1}{2-0}=1562

Now find the derivative of the function; this will be solved for the value(s) found above.

\displaystyle f'(x)=5(2x)(x^2+1)^4

\displaystyle 5(2x)(x^2+1)^4=1562

\displaystyle x=1.484

This value valls within the interval \displaystyle (0,2), validating the mean value theorem.

Example Question #506 : How To Find Differential Functions

Let \displaystyle f(x)=15x^3+23x^2-8x on the interval \displaystyle (1,1.01). Find a value for the number(s) that satisfies the mean value theorem for this function and interval.

Possible Answers:

\displaystyle -3.119

\displaystyle -2.027

\displaystyle 1.002

\displaystyle 1.008

\displaystyle 1.005

Correct answer:

\displaystyle 1.005

Explanation:

The mean value theorem states that for a planar arc passing through a starting and endpoint \displaystyle (a,b);a< b, there exists at a minimum one point, \displaystyle c, within the interval \displaystyle (a,b) for which a line tangent to the curve at this point is parallel to the secant passing through the starting and end points.

Meanvaluetheorem

In other words, if one were to draw a straight line through these start and end points, one could find a point on the curve where the tangent would have the same slope as this line.

\displaystyle f'(c)=\frac{f(b)-f(a)}{b-a}=\frac{Rise}{Run};a< c< b

Note that the value of the derivative of a function at a point is the function's slope at that point; i.e. the slope of the tangent at said point.

First, find the two function values of

\displaystyle f(x)=15x^3+23x^2-8x on the interval \displaystyle (1,1.01)

\displaystyle f(1)=15(1)^3+23(1)^2-8(1)=30

\displaystyle f(1.01)=15(1.01)^3+23(1.01)^2-8(1.01)=30.836815

Then take the difference of the two and divide by the interval.

\displaystyle \frac{30.836815-30}{1.01-1}=83.6815

Now find the derivative of the function; this will be solved for the value(s) found above.

\displaystyle f'(x)=45x^2+46x-8

\displaystyle 45x^2+46x-8=83.6815

\displaystyle x=-2.02722,1.005

To validate the mean value theorem, a solution must fall within the interval used, and \displaystyle 1.005 does in fact fall within \displaystyle (1,1.01)

Example Question #693 : Functions

Find the derivative. 

\displaystyle 2x^2+4x-6

Possible Answers:

\displaystyle 4x+4

\displaystyle 4x+x

\displaystyle 2x+x

\displaystyle 2x+4

Correct answer:

\displaystyle 4x+4

Explanation:

Use the power rule to find the derivative.

\displaystyle \frac{d}{dx}2x^2=4x

\displaystyle \frac{d}{dx}4x=4

\displaystyle \frac{d}{dx}-6=0

Thus, the derivative is \displaystyle 4x+4

Example Question #694 : Functions

Find the derivative.

\displaystyle 6x^3

Possible Answers:

\displaystyle 6x^2

\displaystyle 18x

\displaystyle 18x^2

\displaystyle 12x

Correct answer:

\displaystyle 18x^2

Explanation:

Use the power rule to find the derivative. 

\displaystyle \frac{d}{dx}6x^3=18x^2

Example Question #695 : Functions

Find the derivative at x=3.

\displaystyle 6x^3

Possible Answers:

\displaystyle 204

\displaystyle 162

\displaystyle 64

\displaystyle 18

Correct answer:

\displaystyle 162

Explanation:

First, find the derivative using the power rule:

\displaystyle \frac{d}{dx}6x^3=18x^2

Now, substitute 3 for x.

\displaystyle 18(3^2)=162

Example Question #512 : How To Find Differential Functions

Let \displaystyle f(x)=9^{\cos(x^2)} on the interval \displaystyle (0,0.3). Find a value for the number(s) that satisfies the mean value theorem for this function and interval.

Possible Answers:

\displaystyle 0.29

\displaystyle 0.19

\displaystyle -3.10

\displaystyle 0.02

\displaystyle 1.69

Correct answer:

\displaystyle 0.19

Explanation:

The mean value theorem states that for a planar arc passing through a starting and endpoint \displaystyle (a,b);a< b, there exists at a minimum one point, \displaystyle c, within the interval \displaystyle (a,b) for which a line tangent to the curve at this point is parallel to the secant passing through the starting and end points.

Meanvaluetheorem

In other words, if one were to draw a straight line through these start and end points, one could find a point on the curve where the tangent would have the same slope as this line.

\displaystyle f'(c)=\frac{f(b)-f(a)}{b-a}=\frac{Rise}{Run};a< c< b

Note that the value of the derivative of a function at a point is the function's slope at that point; i.e. the slope of the tangent at said point.

First, find the two function values of

\displaystyle f(x)=9^{\cos(x^2)} on the interval \displaystyle (0,0.3)

\displaystyle f(0)=9^{\cos(0^2)}=9

\displaystyle f(0.3)=9^{\cos(0.3^2)}=8.9203

Then take the difference of the two and divide by the interval.

\displaystyle \frac{8.9203-9}{0.3-0}=-0.266

Now find the derivative of the function; this will be solved for the value(s) found above.

Derivative of an exponential: 

\displaystyle d[a^u]=a^udu\ln(a)

Trigonometric derivative: 

\displaystyle d[\cos(u)]=-\sin(u)du

\displaystyle f'(x)=-2x\sin(x^2)9^{\cos(x^2)}\ln(9)

\displaystyle -2x\sin(x^2)9^{\cos(x^2)}\ln(9)=-0.266

Using a solver, there are multiple solutions which satisfy this equation:

\displaystyle x=-3.54,-3.10,-2.51,-1.85,0.19,1.69,2.51,3.04

However, to satisfy the mean value theorem, a solution must fall within the specified interval. \displaystyle 0.19 falls within \displaystyle (0,0.3).

Example Question #513 : How To Find Differential Functions

As per the mean value theorem, there exists at least one value \displaystyle x=c within the interval \displaystyle (2,b) such that \displaystyle f'(c)=-1. Find \displaystyle b if \displaystyle f(x)=10x-x^2 

Possible Answers:

\displaystyle 4

\displaystyle 2

\displaystyle 9

\displaystyle 7

\displaystyle 5

Correct answer:

\displaystyle 9

Explanation:

The mean value theorem states that for a planar arc passing through a starting and endpoint \displaystyle (a,b);a< b, there exists at a minimum one point, \displaystyle c, within the interval \displaystyle (a,b) for which a line tangent to the curve at this point is parallel to the secant passing through the starting and end points.

Meanvaluetheorem

In other words, if one were to draw a straight line through these start and end points, one could find a point on the curve where the tangent would have the same slope as this line.

\displaystyle f'(c)=\frac{f(b)-f(a)}{b-a}=\frac{Rise}{Run};a< c< b

Using our interval and function definitions, along with the derivative value of \displaystyle f'(c) given, we'll in turn wish to solve for \displaystyle b to validate the mean value theorem:

\displaystyle f'(c)=\frac{f(b)-f(a)}{b-a}

\displaystyle -1=\frac{(10b-b^2)-(10(2)-2^2)}{b-2}

\displaystyle 2-b=10b-b^2-16

\displaystyle b^2-11b+18=0

\displaystyle b=9

(Note that the solution \displaystyle b=2 would not work because it would eliminate the interval as \displaystyle a=2, and it would lead to a zero denominator in the working equation.)

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