how do you integrate cos2x cosx? - The Student Room
cos(2x+x)=cos2x cosx - sin2x sinx cos(2x-x)=cos2x cos x + sin2x sin x so you have two equations cos3x and cos x. Add them together you get 2cos2xcosx = cos3x + cosx divide both sides by two 1/2 (cos3x + cosx) then integrate...