I have learned a lemma that says
For every polynomial $f\in F[x]$ there exists a finite field extension $E\setminus F$ where $f$ is splitted in $E$ and $$[E:F]\leq \deg(f)$$
I wanted to know under what conditions there's an iqualuty $$[E:F]=\deg (f)$$ I guess that a necessary and sufficient condition is that $f$ is irreducible in $F$ and I wanted to ask wheather it's correct.
Thanks.