Solution
= Solution
The <Galois group> acts <transitively> on the $n$ roots because $f$ is <irreducible> and <separable>. The <orbit-stabilizer theorem> gives
$$
\boxed{|G|=n\,|\operatorname{Stab}_G(\alpha_1)|},
$$
so $n$ divides $|G|$. Equivalently, the <tower law> gives $[K:F]=[K:F(\alpha_1)]n$, while the finite <Galois extension> has group order $[K:F]$.