Find the general solution: cos3x + cosx - cos2x = 0

cos3x + cosx - cos2x = 0 → 2cos((3x+x)/2)cos((3x-x)/2) - cos2x = 0 → cos2x(2cosx - 1) = 0 → cos2x = 0, cosx = 1/2 → x = (2n+1)π/4, x = 2nπ ± π/3