The other place negative numbers can pop up in these critters is in the exponent, itself!

5^-2

What kind of math geek hooey is this?!

OK, we know that

5^2 = 5 x 5 = 25

So, what does it mean when the exponent is negative?

It means that we have to do something special...

5^-2 = 1 / 5^2

We make a fraction with the whole thing in the denominator...
and make the exponent positive! 

Yep.  Really.  That's what you do.  Even though it looks weird!

Let's finish it by popping that exponent:

5^-2 = 1 / 5^2 = 1 / 25

Here's another one:

2^-3

Just do the same thing!  Put the whole thing in the bottom of a fraction with a one on top...  and finish it off.

2^-3 = 1 / 2^3 = 1 / 8