Suppose that f(x)=4x+5. What is

Question

f^-1(f^-(9))?

I am pretty sure we can plug in 9 for f(x) which gives us the value of 1. But then we have one more f^-1 but the inverse of 1 is -1. So would the answer be one?

Answer 1

f^-1(x) = (x-5)/4
So,

f^-1(9) = 1
f^-1(1) = -1

So, no, the answer would be -1.