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 7i√13 * 2i√3. Multiplying gives 14i2√39 = −14√39, since i2 = −1. (Note that this time we could combine the radicals as usual, since 13 and 3 are both positive.)