# trig

Prove the identity
sin(3 pi /2 + x) + sin(3pi/2 -x) = -2cosx

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1. L.S = (sin 3pi/2)(cos x) + cos(3pi/2)(sin x) + sin(3pi/2)cos x) + cos(3pi/2)(sin x)
= -cos x + (-cos x), because sin(3pi/2)=-1 and cos(3pi/2) = 0
= -2cos x
= R.S.

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posted by Reiny

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