I know that to show a ring is isomorphic to another ring, I have to find a bijective ring homomorphism between the two rings. Or I could use the F.H.T. but I would also need a function to make that happen (If I'm thinking about it correctly). Do I need to just make up my own function and prove that it is a bijective ring homomorphism? If so, where do I start? Thanks!
Define $f: R[x] \to R$ by $f(p(x))=p(0)$. Prove this is a surjective homomorphism with kernel $(x)$ and use first isomorphism theorem