Hi

I've been trying to prove these pair of functions are inverses:

f(x) = sqrt(16-x^2) and g(x) = -sqrt(16-x^2)

using f(g(x)) = g(f(x)) = x

however when I do the working out it seems i get f(g(x)) = abs(x) BUT g(f(x)) =-abs(x)for some reason. I just did basic substitution n I've checked a few times but I can't seem to resolve this problem.

Could someone please help?