Calculus 1 : Differential Functions

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #621 : Functions

Find the derivative. 

\displaystyle 7x^4+8x^3+9x^2+10x+1

Possible Answers:

\displaystyle 28x^3+24x^2+18x+10

\displaystyle 28x^3+24x^2+18x

\displaystyle 28x^3

\displaystyle 28x^3+24x^2+28x

Correct answer:

\displaystyle 28x^3+24x^2+18x+10

Explanation:

Find the derivative using the power rule. 

Remember the power rule:

\displaystyle (x^n)'=nx^{n-1}

We can now apply this to our situation.

\displaystyle \frac{d}{dx}7x^4=28x^3

\displaystyle \frac{d}{dx}8x^3=24x^2

\displaystyle \frac{d}{dx}9x^2=18x

\displaystyle \frac{d}{dx}10x=10

\displaystyle \frac{d}{dx}1=0

The derivative is \displaystyle 28x^3+24x^2+18x+10

Example Question #621 : Differential Functions

Find the derivative at \displaystyle x=6.

\displaystyle 7x^2-4x

Possible Answers:

\displaystyle 90

\displaystyle 80

\displaystyle 84

\displaystyle 92

Correct answer:

\displaystyle 80

Explanation:

First, find the derivative using the power rule. 

Remember the power rule:

\displaystyle (x^n)'=nx^{n-1}

We can now apply this to our situation.

\displaystyle \frac{d}{dx}7x^2=14x

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

The derivative is \displaystyle 14x-4

Now, substitute \displaystyle 6 for \displaystyle x.

\displaystyle 14(6)-4=80

Example Question #622 : Differential Functions

Find the derivative. 

\displaystyle 5x\cos (x)

Possible Answers:

\displaystyle -x\sin (x)+5\cos (x)

\displaystyle -5x\sin (x)-5\cos (x)

\displaystyle 5x\sin (x)+5\cos (x)

\displaystyle -5x\sin (x)+5\cos (x)

Correct answer:

\displaystyle -5x\sin (x)+5\cos (x)

Explanation:

Use the product rule to find the derivative.

Remember the product rule:

\displaystyle (f(x)g(x))'=f'(x)g(x)+f(x)g'(x)

We can now apply this to our situation.

\displaystyle 5x(-\sin(x))+\cos (x)(5)

Simplify.

\displaystyle -5x\sin (x)+5\cos (x)

Example Question #621 : Functions

Find the derivative.

\displaystyle \frac{-1}{x+2}

Possible Answers:

\displaystyle 0

\displaystyle \frac{1}{x+2}

\displaystyle \frac{-1}{(x+2)^2}

\displaystyle 1

Correct answer:

\displaystyle \frac{-1}{(x+2)^2}

Explanation:

Use the quotient rule to find the derivative. 

Remember the quotient rule:

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

We can now apply this to our situation.

\displaystyle \frac{x+2(0)-(-1)1}{(x+2)^2}

\displaystyle =\frac{-1}{(x+2)^2}

Example Question #431 : How To Find Differential Functions

Find the derivative.

\displaystyle \frac{5}{x^2}

Possible Answers:

\displaystyle \frac{10}{x^4}

\displaystyle \frac{5}{x^4}

\displaystyle \frac{10}{x^3}

\displaystyle \frac{5}{x^3}

Correct answer:

\displaystyle \frac{10}{x^3}

Explanation:

Find the derivative using the quotient rule. 

Remember the quotient rule:

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

We can now apply this to our situation.

\displaystyle \frac{x^2(0)-5(2x)}{x^4}

\displaystyle =\frac{10x}{x^4}=\frac{10}{x^3}

Example Question #431 : Other Differential Functions

Find the derivative. 

\displaystyle \frac{x^2}{3}

Possible Answers:

\displaystyle \frac{2x}{3}

\displaystyle \frac{2x}{9}

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

\displaystyle \frac{x}{9}

Correct answer:

\displaystyle \frac{2x}{3}

Explanation:

Find the derivative using the quotient rule. 

Remember the quotient rule:

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

We can now apply this to our situation.

\displaystyle \frac{d}{dx}\frac{x^2}{3}=\frac{3(2x)-x^2(0)}{9}

\displaystyle =\frac{6x}{9}=\frac{2x}{3}

Example Question #1656 : Calculus

Let \displaystyle f(x)=x^5+7x 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 -0.89

\displaystyle 1.17

\displaystyle -1.17

\displaystyle 0.89

\displaystyle 1.33

Correct answer:

\displaystyle 1.33

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^5+7x on the interval \displaystyle (0,2)

\displaystyle f(0)=0^5+7(0)=0

\displaystyle f(2)=2^5+7(2)=46

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

\displaystyle \frac{46-0}{2-0}=23

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

\displaystyle f'(x)=5x^4+7

\displaystyle 5x^4+7=23

\displaystyle x=-1.33,1.33

The solution \displaystyle x=1.33 validates the mean value theorem by falling within \displaystyle (0,2)

Example Question #1657 : Calculus

Let \displaystyle f(x)=x^{10}-\frac{1}{x^{10}} on the interval \displaystyle (0.9,1). Find a value for the number(s) that satisfies the mean value theorem for this function and interval.

Possible Answers:

\displaystyle 0.98

\displaystyle 1.03

\displaystyle 1.09

\displaystyle 0.94

\displaystyle 0.91

Correct answer:

\displaystyle 0.94

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^{10}-\frac{1}{x^{10}} on the interval \displaystyle (0.9,1)

\displaystyle f(0.9)=0.9^{10}-\frac{1}{0.9^{10}}=-2.519

\displaystyle f(1)=1^{10}-\frac{1}{1^{10}}=0 

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

\displaystyle \frac{0-(-2.519)}{1-0.9}=25.19

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

\displaystyle f'(x)=10x^9+\frac{10}{x^{11}}

\displaystyle 10x^9+\frac{10}{x^{11}}=25.19

\displaystyle x=0.94,1.09

Of these two solutions \displaystyle x=0.94 validates the mean value theorem by valling within \displaystyle (0.9,1)

Example Question #621 : Functions

Let \displaystyle f(x)=x^3+sin(2x)+cos(3x) on the interval \displaystyle (0,1). How many values of x exist that satisfy the mean value theorem for this function and interval?

Possible Answers:

\displaystyle 0

\displaystyle 2

\displaystyle 3

\displaystyle 1

\displaystyle 4

Correct answer:

\displaystyle 2

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^3+sin(2x)+cos(3x) on the interval \displaystyle (0,1)

\displaystyle f(0)=0^3+sin(2(0))+cos(3(0))=1

\displaystyle f(1)=1^3+sin(2(1))+cos(3(1))=0.919

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

\displaystyle \frac{0.919-1}{1-0}=-0.081

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

\displaystyle d(sin(u))=cos(u)du;d(cos(u))=-sin(u)du

\displaystyle f'(x)=3x^2+2cos(2x)-3sin(3x)

\displaystyle 3x^2+2cos(2x)-3sin(3x)=-0.081

\displaystyle x=0.247,0.811

Both of these solutions validate the mean value theorem by falling within \displaystyle (0,1).

Note that for a function that's differentiable on an interval like the one given, there will always be at least one point that satisfies the MVT.

Example Question #1652 : Calculus

Let \displaystyle f(x)=4x-sin(5x) on the interval \displaystyle (0,\pi). How many values of x such that the mean value theorem is validated?

Possible Answers:

\displaystyle 8

\displaystyle 9

\displaystyle 10

\displaystyle 12

\displaystyle 11

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

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)=4x-sin(5x) on the interval \displaystyle (0,\pi)

\displaystyle f(0)=4(0)-sin(5(0))=0

\displaystyle f(\pi)=4\pi-sin(5\pi)=4\pi

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

\displaystyle \frac{4\pi-0}{\pi-0}=4

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

\displaystyle d(sin(u))=cos(u)du

\displaystyle f'(x)=4-5cos(5x)

\displaystyle 4-5cos(5x)=4

\displaystyle cos(5x)=0

\displaystyle 5x=cos^{-1}(0)

\displaystyle 5x=\frac{\pi}{2}n ;n:integer

\displaystyle x=\frac{\pi}{10}n ;n:integer \neq 0

Note that we do not include the start and end points as values that satisfy the mean value theorem. Therefore, there are nine values which fall within the open interval \displaystyle (0,\pi) and satisfy the MVT \displaystyle (n=[1,9])

 

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