# Question about inverse functions

1. Jul 31, 2008

### Spirochete

If you've already found that F(g(X))=X, is it necessarry to also prove that g(f(X))=X to know that you have inverse functions? Would there be a case where the first statement is true but the second is false?

2. Jul 31, 2008

### MeJennifer

The inverse of many functions are not functions themselves.

3. Jul 31, 2008

### HallsofIvy

Staff Emeritus
In particular, if $f(x)= x^2$] and $g(x)= \sqrt{x}$, $f(g(x))= (\sqrt(x))^2= x$ but $g(f(x))= \sqrt{x^2}= |x|$. Of course, if the domain of f is restricted to the non-negative numbers, then they are inverses.