Possible Duplicate:
Ring such that $x^4=x$ for all $x$
Let $R$ be a ring such that $a^4=a$ $ ,\forall a \in R$. How do I show that $R$ is commutative?
Possible Duplicate:
Ring such that $x^4=x$ for all $x$
Let $R$ be a ring such that $a^4=a$ $ ,\forall a \in R$. How do I show that $R$ is commutative?