I need to write a proof for class and I'm having a lot of trouble getting started. Maybe someone here can help me.

Problem:

Leta,m,nbe integers andd=gcd(m,n). Ifmdividesanandddividesa, thenmdividesa.^{2}

(Is there a way to use LaTeX on this forum?)

My Thoughts:

I know we must use Bezout's Identity to solve this. So far I have that since d=gcd(m,n) and d|a, there exist integers r and s such that mr + ns = a.

That is all I have, and I really cannot for the life of me see what I'm supposed to do next. Does anybody see where I need to go from here?