Can anyone shed light on how the following simplification was achieved?

I had:

Which became:

I expect there is a trig identity required but my mind is blank, help!

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- Oct 16th 2011, 05:58 PMYoungMarbleGiantSimplifying an equation
Can anyone shed light on how the following simplification was achieved?

I had:

Which became:

I expect there is a trig identity required but my mind is blank, help! - Oct 16th 2011, 06:34 PMSammySRe: Simplifying an equation
To simplify things, look at

=

- Oct 16th 2011, 07:10 PMYoungMarbleGiantRe: Simplifying an equation
Got it, thank you very much.