Solution
= Solution
An irreducible degree-$n$ polynomial over $\mathbb F_q$ is separable and its roots lie in $\mathbb F_{q^n}$, with any one root generating that field. Hence its splitting field is $\mathbb F_{q^n}$ and
$$
\boxed{\operatorname{Gal}(f)\cong C_n},
$$
generated by the <Frobenius endomorphism>[Frobenius automorphism] $x\mapsto x^q$.