Hello, Im trying to prove that the product of two non principal ideals is a principal ideal.

I consider the non principals ideals $\displaystyle $\left( {3,1 - \sqrt { - 5} } \right),\left( {3,1 + \sqrt { - 5} } \right) \in \mathbb{Z}\left[ {\sqrt { - 5} } \right]$$

The book saids the result is (3). But I don`t know how to do the product.

Regards...