Question

Let f(x) = 4x + 7. Find f-1(15)

Answer 1

`f(x)=4x+7`

1. replace f(x) with y

`y=4x+7`

2. Replace every x with a y and replace every y with an x

`x=4y+7`

3. Solve for y:

`\begin{gathered} 4y=x-7 \\ y=(x-7)/(4) \end{gathered}`

4. Replace y with f−1(x):

`f^(-1)(x)=(x-7)/(4)`

Evaluate the inverse for x = 15:

`f^(-1)(15)=(15-7)/(4)=(8)/(4)=2`