Diophantine equation?

Let $x$ and $n$ be two positive integers. Now the polynomial $P(y)=2y^2-y\sqrt{(x-m)(x+m)}+x$ is perfect square for any positive integer $y$ where $m$ is a nonnegative integer. If $P(n)=0$ what is the value of $m+n+x$?

Equation

0 Upvote 0 Downvote