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# Prove the following identities: 4cos4xcos2xcosx= cos7x+cos5x+cos3x+cosx?

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- Anonymous1 decade agoFavorite Answer
H = cos7x + cos5 x + cos 3x + cos x = (cos7x + cos x) + (cos5 x + cos 3x)

H = 2 cos 4x cos 3x + 2 cos 4x cos x

H = (2 cos 3x + cos x) cos 4x

H = (2 * 2 cos 2x cos x) cos 4x

H = 4 cos x cos 2x cos 4x

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