原式= 1/2 - 1/2cos2x + 1/2 - 1/2cos(2x+4π/3) + 1/2 - 1/2cos(2x-4π/3) = 3/2 - 1/2cos2x - 1/2cos2xcos(4π/3) + 1/2sin2xsin(4π/3) -1/2cos2xcos4π/3 - 1/2sin2xsin4π/3 = 3/2 - 1/2cos2x + 1/4cos2x - √3/4sin2x + 1/4cos2x + √3/4sin2x = 3/2