Let $F$ be a field of characteristic $p>0$, and let $E/F$ be a Galois extension with cyclic galois group $\langle \sigma \rangle$ of order $p$.
I want to prove that $E=F(\alpha)$, where $\alpha$ is a root of an irreducible polynomial in $F[x]$ of the form $x^p-x-c$. I know that this polynomial is irreducible if and only it don't has roots on F. Any idea about how I can prove this?
It is an exercice of Rotman, Galois theory