Hello there!
In order to find the inverse, we need to interchange the variables and solve for y.
[tex]f ^{-1} (x) = \sqrt{-4+x} , - \sqrt{-4+x} [/tex]
Edited: Yes the inverse is a function.
What is a function?
A function is a special relationship where each input has a single output.
It is often written as "f(x)" where x is the input value.
Best of luck!