Mark M. answered 02/10/21
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Retired math prof. Very extensive Precalculus tutoring experience.
cos(3x) = cos(2x + x) = cos(2x)cosx - sin(2x)sinx
= (cos2x - sin2x)cosx - 2sinxcosxsinx = cos3x - sin2xcosx - 2sin2xcosx = cos3x - 3sin2xcosx
Elif I.
wow I got it now, thank you a lot!02/10/21