How is the following statement true?
If $m$ and $n$ are positive integers with $m > n$. Let $a = 2mn, b = m^2 - n^2$ and $c = m^2 + n^2$ be the sides of a Pythagorean triangle. Then the radius of the in-circle $r$ is given by the integer $r = n (m-n)$.
Thanks!