用分部积分法 ∫xsin^2xdx=0.5∫x(1-cos2x)dx =0.5∫xdx-0.25∫xdsin2x =0.25x^2-0.25xsin2x+0.25∫sin2xdx =0.25x^2-0.25xsin2x-0.125cos2x+C
=∫x[(1-cos2x)/2]dx=1/4(x^2-∫xdsin2x)=1/4(x^2-xsin2x+∫sin2xdx)=x^2/4-(xsin2x)/4-(cos2x)/8+C