# Trig identity problem?

Can someone solve this step by step?

(sin x + sin3x)/ (cos x + cos 3x) = tan 2x

Show all your work and don't skip steps please. If you skip steps you will not be voted best answer.

### 1 Answer

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- grunfeldLv 77 years agoFavorite Answer
LHS = ( sin x + sin 3x) / ( cos x + cos 3x )

LHS = 2 sin ( 2x) cos (x) / 2 cos (2x ) cos ( x )

LHS = tan 2x

LHS = RHS

QED

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