Simplifying an expression

exequor

can someone explain to me the stages that are missing in the expression in the attached picture. i think that it has to do with identities but in the book that i got it from did not explain clearly how they went from one line to another. i will appreciate the help very much.

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gnome

It uses this identity:

[tex]sin(x)cos(y) = \frac{1}{2}\left(sin(x+y) + sin(x-y)\right)[/tex]

[tex] x = \theta[/tex]
[tex] y = \theta - 30^o[/tex]

exequor

thanx very much gnome i thought that i would never get a response