(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

I am reviewing some old exam solutions and came across something I cannot figure out. I'm don't understand how they simplify from the first equation to the second. I looked up a table of trig identies but could not find anything that would help.

2. Relevant equations

http://img296.imageshack.us/img296/864/untitledimageda3.th.jpg [Broken]

3. The attempt at a solution

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# Homework Help: Trouble simplifying

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