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Prove that cos3x = 4cos3 x -3cosx . |
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Answer» cos3x = cos(2x + x) = cos2x cos x – sin2xsinx = (2cos2x - 1)cosx – 2sinxcosxsinx = 2cos3x - cosx - 2cosx(1 - cos2x) = 4cos3 x - 3cosx |
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