A base that is raised to a negative exponent has an integral exponent. 

The general rule for when a base is raised to a negative exponent This is because exponents have a pattern of being divisible by the base, so if continued past exponent 0, you begin to get fractions

You flip it from the numerator to the denominator or the denominator to the numerator. This flip makes the exponent go from a negative exponent to a positive exponent. 

This law remains the same for evaluating different expression

When there are numbers with positive exponents and negative exponents, only the bases with the negative exponents need to move.

The general rule of fraction base to a negative exponent is

This is because 

Evaluating an expression with a fraction for a base and a negative exponent 

You flip the fraction to make the outer negative exponent, a positive exponent. Then proceed to continue simplifying

This unit was very challenging, it called for many different exponent laws for different situations. Once it is explained, though, and I figured out when to use which exponent law, I got the hang of it. When many different of these exponent laws are seen in the same expression, it may seem over whelming to simplify or evaluate, but if you follow through with each law, it become quite easy.