x(sinx)^2=x*(1-cos2x)/2=1/2*x-1/2xcos2x
∫x(sinx)^2dx=1/2∫xdx- 1/2∫xcos2xdx
=1/4x^2 -1/4∫xdsin2x
=1/4x^2-1/4(xsin2x-∫sin2xdx)
=1/4x^2-1/4xsin2x+1/4∫sin2xdx
=1/4x^2-1/4xsin2x-1/8cos2x+c