Precalculus : Find the Inverse of a Function

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Inverse Functions

Find the inverse of,

 \displaystyle 3x+1=y.

Possible Answers:

\displaystyle x=\frac{y-1}{3}

\displaystyle y=\frac{x+1}{3}

\displaystyle y=\frac{x-1}{3}

\displaystyle x=3y+1

Correct answer:

\displaystyle y=\frac{x-1}{3}

Explanation:

In order to find the inverse, switch the x and y variables in the function then solve for y.

\displaystyle 3x+1=y

Switching variables we get,

 \displaystyle 3y+1=x.

 Then solving for y to get our final answer.

\displaystyle 3y=x-1

\displaystyle y=\frac{x-1}{3}

Example Question #1 : Inverse Functions

Find the inverse of,

\displaystyle y=x^{2}.

Possible Answers:

\displaystyle y=\pm\sqrt{x}

\displaystyle y=\frac{x}{2}

\displaystyle x=y^{2}

\displaystyle x=\pm \sqrt{y}

Correct answer:

\displaystyle y=\pm\sqrt{x}

Explanation:

First, switch the variables making \displaystyle y=x^2 into \displaystyle x=y^{2}.

Then solve for y by taking the square root of both sides.

\displaystyle y^2=x

\displaystyle \sqrt {y^2}=\pm \sqrt x

\displaystyle y=\pm \sqrt x

 

Example Question #1 : Find The Inverse Of A Function

Find the inverse of the following equation.

\displaystyle y=\sqrt{\ln(x)+2}.

Possible Answers:

\displaystyle y=\pm x^2 -2

\displaystyle y=e^x+2

\displaystyle y=x-2

\displaystyle y=e^\pm ^{^{x^2}-2}

\displaystyle y=e^x^{^{2}-2}

Correct answer:

\displaystyle y=e^x^{^{2}-2}

Explanation:

To find the inverse in this case, we need to switch our x and y variables and then solve for y.

Therefore,

\displaystyle y=\sqrt{\ln(x)+2} becomes,

\displaystyle x=\sqrt{\ln(y)+2}

To solve for y we square both sides to get rid of the sqaure root.

\displaystyle x^2=\ln(y)+2

We then subtract 2 from both sides and take the exponenetial of each side, leaving us with the final answer.

\displaystyle x^2-2=\ln(y)

\displaystyle e^{x^2-2}=e^{\ln(y)}

\displaystyle e^x^{^{2}-2}=y

 

Example Question #4 : Matrices

Find the inverse of the following function.

\displaystyle y=x^3+e^0

Possible Answers:

\displaystyle y^{-1}=\sqrt[3]{x+e}

\displaystyle y^{-1}=1-x^{3}}

\displaystyle y^{-1}=\sqrt[{3}]{x-1}

\displaystyle y^{-1}=e^{0}}

Correct answer:

\displaystyle y^{-1}=\sqrt[{3}]{x-1}

Explanation:

To find the inverse of y, or 

\displaystyle y^{-1}

first switch your variables x and y in the equation. 

 \displaystyle x_{i}=y_i^3+e^0

Second, solve for the variable \displaystyle y_i in the resulting equation. 

\displaystyle x_i-e^0=y_i^3

\displaystyle (x_i-e^0)^\frac{1}{3}=(y_i^{3})^\frac{1}{3}

\displaystyle y_i=\sqrt[3]{x_i-e^0}

Simplifying a number with 0 as the power, the inverse is

\displaystyle y^{-1}=\sqrt[{3}]{x-1}

Example Question #181 : Algebra

Find the inverse of the following function.

\displaystyle y=\ln\, x\: +\: \pi

Possible Answers:

\displaystyle y^{-1}=\pi-\ln(x)

\displaystyle y^{-1}=e^{x-\pi}

\displaystyle y^{-1}=\ln(y)-\pi

Does not exist

Correct answer:

\displaystyle y^{-1}=e^{x-\pi}

Explanation:

To find the inverse of y, or 

\displaystyle y^{-1}

first switch your variables x and y in the equation. 

\displaystyle x_i=\ln(y_i)+\pi

Second, solve for the variable \displaystyle y_i in the resulting equation. 

\displaystyle x_i-\pi=\ln\,y_i

And by setting each side of the equation as powers of base e,

\displaystyle y^{-1}=e^{x-\pi}

Example Question #1 : Inverses

Find the inverse of the function.

\displaystyle y=x+5

Possible Answers:

\displaystyle y^{-1}=5-x

\displaystyle y^{-1}=5+x

\displaystyle y^{-1}=-x-5

\displaystyle y^{-1}=x-5

Correct answer:

\displaystyle y^{-1}=x-5

Explanation:

To find the inverse we need to switch the variables and then solve for y.

\displaystyle y=x+5

Switching the variables we get the following equation,

\displaystyle x=y+5.

Now solve for y.

\displaystyle y^{-1}=x-5

Example Question #1044 : Pre Calculus

Find the inverse of 

\displaystyle y=10x+9

Possible Answers:

\displaystyle y=9x-10

\displaystyle y=\frac{9x}{10}

\displaystyle y=9x+10

\displaystyle y=10x

\displaystyle y=\frac{x-9}{10}

Correct answer:

\displaystyle y=\frac{x-9}{10}

Explanation:

So we first replace every \displaystyle y with an \displaystyle x and every \displaystyle x with a \displaystyle y.

Our resulting equation is:

\displaystyle x=10y+9

 

Now we simply solve for y.

Subtract 9 from both sides:

\displaystyle x-9=10y+9-9

\displaystyle x-9=10y

Now divide both sides by 10:

\displaystyle \frac{x-9}{10}=\frac{10y}{10}

\displaystyle \frac{x-9}{10}=y

 

The inverse of

\displaystyle y=10x+9

is

\displaystyle y=\frac{x-9}{10}

Example Question #1045 : Pre Calculus

What is the inverse of

\displaystyle y=9x

Possible Answers:

\displaystyle y=\frac{x}{9}

\displaystyle x=0

\displaystyle y=0

\displaystyle y=x

\displaystyle y=9x

Correct answer:

\displaystyle y=\frac{x}{9}

Explanation:

To find the inverse of a function we just switch the places of all \displaystyle x and \displaystyle y with eachother.

So

\displaystyle y=9x

turns into

\displaystyle x=9y

 

Now we solve for \displaystyle y

Divide both sides by \displaystyle 9

\displaystyle \frac{x}{9}=\frac{9y}{9}

\displaystyle y=\frac{x}{9}

Example Question #181 : Algebra

If \displaystyle f(x)=-\frac{3x}{5}+11, what is its inverse function, \displaystyle f^{-1}(x)?

Possible Answers:

\displaystyle f^{-1}(x)=-\frac{3x}{5}-\frac{33}{5}

\displaystyle f^{-1}(x)=-\frac{5x}{3}-\frac{55}{3}

\displaystyle f^{-1}(x)=\frac{5x}{3}+\frac{55}{3}

\displaystyle f^{-1}(x)=-\frac{3x}{5}+\frac{33}{5}

\displaystyle f^{-1}(x)=-\frac{5x}{3}+\frac{55}{3}

Correct answer:

\displaystyle f^{-1}(x)=-\frac{5x}{3}+\frac{55}{3}

Explanation:

We begin by taking \displaystyle f(x)=-\frac{3x}{5}+11 and changing the \displaystyle f(x) to a \displaystyle y, giving us \displaystyle y=-\frac{3x}{5}+11.

Next, we switch all of our \displaystyle x's and \displaystyle y's, giving us \displaystyle x=-\frac{3y}{5}+11.

Finally, we solve for \displaystyle y by subtracting \displaystyle 11 from each side, multiplying each side by \displaystyle 5, and dividing each side by \displaystyle -3, leaving us with,

 \displaystyle y=-\frac{5x}{3}+\frac{55}{3}.

Example Question #1 : Find The Inverse Of A Function

Find the inverse of \displaystyle y =10x-1.

Possible Answers:

\displaystyle y = 10x+1

\displaystyle x=10y+1

\displaystyle y = \frac{x-1}{10}

\displaystyle x = \frac{y - 1}{10}

\displaystyle y = \frac{x+1}{10}

Correct answer:

\displaystyle y = \frac{x+1}{10}

Explanation:

To find the inverse of the function, we switch the switch the \displaystyle x and \displaystyle y variables in the function.

\displaystyle y = 10x-1

Switching \displaystyle x and \displaystyle y gives

\displaystyle x = 10y -1

Then, solving for \displaystyle y gives our answer:

\displaystyle x + 1 = 10y

\displaystyle \frac{x-1}{10} = y

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