用分部积分法：∫x(lnx)^2dx=(1/2)x^2(lnx)^2-∫(1/2)x^2*(1/x)dx=(1/2)x^2(lnx)^2-∫(1/2)xdx=(1/2)x^2(lnx)^2-(1/4)x^2+C
