解： ∫xsinxcosxdx=1/2 ∫xsin2xdx=1/2 [-x(cos2x)/2+1/2 ∫cos2xdx]=-x(cos2x)/4+1/8 sin2x+C
∫xsinxcosxdx＝1/2∫xsin2xdx=-1/4∫xdcos2x=-1/4（xcos2x-∫cos2xdx）=-1/4xcos2x 1/8sin2x C
