please solve this question. this is urgent.
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cos 3x
=cos (2x+x)
=cos2x cosx - sin2x sinx
=(2cos²-1)cox - 2sinx cosx (sinx)
=2cos³x-cosx - 2cosx sin²x
=2cos³x - cosx - 2cosx (1-cos²x)
=2cos³x - cosx - 2cosx + 2cos³x
=4cos³x - 3cosx
=cos (2x+x)
=cos2x cosx - sin2x sinx
=(2cos²-1)cox - 2sinx cosx (sinx)
=2cos³x-cosx - 2cosx sin²x
=2cos³x - cosx - 2cosx (1-cos²x)
=2cos³x - cosx - 2cosx + 2cos³x
=4cos³x - 3cosx
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