分部积分
∫（x*sin2x）dx
=(1/2)∫（x*sin2x）d2x
=-(1/2)∫x*dcos2x
=-(1/2)xcos2x+(1/2)∫cos2xdx
=-(1/2)xcos2x+(1/4)∫cos2xd2x
=-(1/2)xcos2x+(1/4)sin2x+C