You may want to review imaginary numbers and multiplying roots first.

When multiplying the roots of two negative numbers, you need to
be careful, since the rules you're used to don't quite work. For
example, suppose you need to multiply
√(−637)*√(−12). If you try to combine them
into √7644 = 14√39, you'll be wrong; that doesn't work
if the numbers under the root signs are negative. You need to
simplify both roots individually first, getting 7*i*√13
* 2*i*√3. Multiplying gives
14*i*^{2}√39 = −14√39,
since *i*^{2} = −1. (Note that this time
we *could* combine the radicals as usual, since 13 and 3
are both positive.)