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prove: cos3x-cosx=4cos^3x-4cosx

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I just need to prove that the one side equals the other using the trigonometric identities. Thanks for your help!

trigonometric-identities

asked Nov 30, 2013 in TRIGONOMETRY by dkinz Apprentice

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1 Answer

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Remeber the formula cos3A = 4cos^3A-3cosA

Lefthand side = cos3x-cosx

= 4cos^3x-3cosx-cosx

= 4cos^3x-4cosx

= Right hand side.

answered Dec 13, 2013 by friend Mentor

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