# Math Help - Isomorphic groups

1. ## Isomorphic groups

Let f: G --> H be an isomorphism, G and H are groups.
I've already showed that for every x in G, |f(x)| = |x|. (|x| = order of x, the smallest positive integer such that $x^n$ is the identity element)

How to show that any two isomorphic groups have the same number of elements of n, where n is any positive integer?