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(sin 3x + sin x) sin x + (cos 3x - cos x) cos x = 0
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Answer:
L.H.S,
(sin3x+sinx)sinx+(cos3x-cosx)cosx
= sin3x sinx+sin²x +cos3x cos x -cos²x
= (cos 3x cos x+sin3x sinx) -(cos ²x -sin ²x)
=cos (3x-x) -cos2x
=cos2x -cos2x
=0
L.H.S=R.H.S (proved)
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