# Idempotent Elements of a Commutative Ring

I have to prove this statement and I'm a bit unsure how to go about it:

Show that the set of all idempotent elements of a commutative ring is closed under multiplication. Furthermore, find all the idempotent elements in the ring ${\bf Z}_6 \times {\bf Z}_{12}$.

So, I know that the proof should start off with saying that an element a of a ring $R$ is idempotent if $a^2 = a$. I'm not sure how to show that the set of all idempotent elements is closed under multiplication. Any help with the proof would be appreciated.

• $(ab)^2 = a^2b^2$ since the ring is commutative. – Prahlad Vaidyanathan May 8 '14 at 3:05

(2)$(a,b)(a,b)=(a^2,b^2)$