(cosx)^4=(cosx^2)^2=(0.5cos2x+0.5)^2=0.25(cos2x)^2+0.5cos2x+0.25=0.25(1/2cos4x+1/2)+0.5cos2x+0.25=1/8cos4x +1/4cos2x +3/8积分得到1/32 sin4x +1/8 sin2x +3/8 x代入上下限π/2和0定积分值=3π/16
