Let F_q[X]$\mathbb{F}_q[X]$ be the polynomial ring over the finite field with q$q$ elements. Let f$f$ be a polynomial of the form x^n-a$x^n-a$ and let g$g$ be a polynomial of the form x^m-b$x^m-b$. Is it known whether gcd(f,g)$\operatorname{gcd}(f,g)$ is of the same form, i.e. x^k-c$x^k-c$, for some k$k$,c$c$? Thanks in advance.
Post Closed as "Not suitable for this site" by Andrés E. Caicedo, Alex Degtyarev, Myshkin, Franz Lemmermeyer, Felipe Voloch