Rationalizing the denominator of a radical fraction

This is for my trigonometry class but it's only a small portion of a bigger problem so I'm posting it here. Here is a picture of my issue:

http://i.imgur.com/cfxLe.png

How can I get that final answer? I know to rationalize a denominator I have to multiply both sides by the bottom radical, but that one seems more complicated. Help is appreciated.

Re: Rationalizing the denominator of a radical fraction

Re: Rationalizing the denominator of a radical fraction

General:

(a - b) / (a + b) = (a^2 - 2ab + b^2) / (a^2 - b^2)

Your a is 15, your b is 7SQRT(15); throw 'em in there !