Question 74151
The rule is:
{{{highlight(a^(-n)=1/a^n)}}}
The negative in the exponent effects whether the base becomes a numerator or denominator.  If it's a denominator and it has a negative exponent it becomes a numerator with a positive exponent.  If it's a numerator with a negative exponent, it becomes a denominator with a positive exponent.
It also depends on how it is written:
{{{(3*5)^(-1)}}}
{{{(15)^(-1)}}}
{{{highlight(1/15)}}}
But if it is written like this:
{{{3*5^(-1)}}}
{{{3(1/5)}}}
{{{highlight(3/5)}}}
I hope that answers your question.
Happy Calculating!!!!