Answer:
f(x) = -5x - 4
Explanation:
We want to get the inverse of the following function:
f^-1(x) = (-1/5)x - 4/5
To do that, we have to replace x with f(x) and f^-1(x) with x, as follows:
x = (-1/5)f(x) - 4/5
And then solve for f(x), the inverse of f^-1(x).
x + 4/5 = (-1/5)f(x)
f(x) = -5x + (-5)4/5
f(x) = -5x - 4
To check our result we compute a pair (x, f(x))
x f(x)
1 -5*1 - 4 = -9
which has to be equivalent to (-9, 1) in the original function
x f^-1(x)
-9 (-1/5)*(-9) - 4/5 = 1