Solution
= Solution
If a power of $a$ lies in $I\cap J$, then $a\in\sqrt I\cap\sqrt J$. Conversely, if $a^m\in I$ and $a^n\in J$, the power $a^{\max(m,n)}$ lies in both ideals. Therefore \b[$\sqrt{I\cap J}=\sqrt I\cap\sqrt J$] for any commutative ring.