TITLE: Exhibiting an isomorphism between two finite fields
QUESTION [7 upvotes]: So I want to find the isomorphism $\phi$ that takes $F = \mathbb{Z}_3/\langle x^3 - x - 1\rangle$ to $E = \mathbb{Z}_3/\langle x^3 - x + 1\rangle$.  I understand that these are both finite fields of size 3^3 since $x^3 - x - 1$ and $x^3 - x + 1$ are both irreducible polynomials of degree 3.  I feel like a good start would be to take the subfield $\mathbb{Z_3}$ in $F$ to the subfield $\mathbb{Z_3}$ in $E$.  Or maybe find the right generator of each multiplicative group of size $3^3-1$ of each field and send those to each other.

REPLY [3 votes]: If $P(x)=x^3-x+1$ and $Q(x)=x^3-x-1$, then $P(-x)=-Q(x)$, so try 
$$x+\langle x^3-x+1\rangle\mapsto -x+\langle x^3-x-1\rangle.$$