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Prove the identity: sin 4x = 4 sin x cos3 x – 4 cos x sin3 x |
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Answer» Let us consider the LHS sin 4x As we know, sin 2x = 2 sin x cos x cos 2x = cos2 x – sin2 x Therefore, sin 4x = 2 sin 2x cos 2x = 2(2 sin x cos x) (cos2 x – sin2 x) = 4 sin x cos x (cos2 x – sin2 x) = 4 sin x cos3 x – 4 sin3 x cos x = RHS Thus proved. |
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