∫(xcos2x)dx
=(1/2)∫xdsin2x
=(1/2)xsin2x-(1/2)∫sin2xdx
=(1/2)xsin2x-(1/4)∫sin2xd2x
=(1/2)xsin2x+(1/4)cos2x+C
∫(xcos2x)dx分部积分
∫(xcos2x)dx
=(1/2)∫xdsin2x
=(1/2)xsin2x-(1/2)∫sin2xdx
=(1/2)xsin2x-(1/4)∫sin2xd2x
=(1/2)xsin2x+(1/4)cos2x+C