∫xtan^2xdx= ∫x(sec^2x-1)dx=∫xdtanx-∫xdx=xtanx-∫tanxdx-(1/2)x^2=xtanx+ln|cosx|-(1/2)x^2+c∫xsinxcosxdx= (1/2)∫xdsin2x=(1/2)xsin2x-(1/2)∫sin2xdx=(1/2)xsin2x+(1/4)cos2x+c.
