Question

what is the inverse ƒ(x) = x2 - 9

Answer 1

The inverse function is what you have to do to f(x) (which I will call y) to get x.

y + 9 = x^2
x = sqrt(y + 9)

Now switch variables and call it the inverse function of f(x)

f^-1(x) = sqrt(x + 9)