Negative x Negative

I'm not really sure, I would explain it as one of those math things "that just works." And don't question it. :) It probably would be hard to explain because it would be hard to represent a negative of something like you can a positive number in an example.

EDIT: Not sure if this would help explain: http://www.mathsisfun.com/multiplying-negatives.html

Here is a quote from the link stated above this is the best explanation about it that I could find:

Why does multiplying two negative numbers make a positive? Well, first there is the "common sense" explanation:

If I say "Eat!" I am encouraging you to eat (positive), but if I say "do not eat!" I am saying the opposite (negative).

Now if I say "Do NOT not eat", I am saying I don't want you to starve, so I am back to saying "Eat!".

So, two negatives make a positive, and if that satisifes you, then you don't need to read any more.

Basically I think of it like this a negative is have an addition sign when it comes to multiplication and it looking to become positive. I know this doesn't necessarily answer your question but if your struggling with the concept than this might help you.