Question

Which function is the inverse of f(x) = –5x – 4?

A) f-1(x)=-5x-4
B) f-19(x)=-1/5x+4/5
C) f-1(x) = –4x + 5
D) f-1(x) = 4x + 4

Answer 1

Just took the test. A is the right answer. 

Answer 2

`f^(-1)(x)=-(1)/(5)x-(4)/(5)`

Explanation:

we have

`f(x)=-5x-4`

Let

`y=f(x)`

`y=-5x-4`

Step 1

Exchange the variables x for y and y for x

`x=-5y-4`

Step 2

Isolate the variable y

`x=-5y-4`

`5y=-x-4`

`y=-(1)/(5)x-(4)/(5)`

Step 3

Let

`f^(-1)(x)=y`

`f^(-1)(x)=-(1)/(5)x-(4)/(5)`