分步积分吧
∫x*(cos^2x)dx
=1/2∫x*(1+cos2x)dx
=1/4x^2+1/2∫x*cos2xdx
=1/4x^2+1/4∫x*dsin2x
=1/4x^2+1/4x*sin2x-1/4∫sin2xdx
=1/4x^2+1/4x*sin2x+1/8cos2x+C
∫x*(cos^2x)dx
分步积分吧
∫x*(cos^2x)dx
=1/2∫x*(1+cos2x)dx
=1/4x^2+1/2∫x*cos2xdx
=1/4x^2+1/4∫x*dsin2x
=1/4x^2+1/4x*sin2x-1/4∫sin2xdx
=1/4x^2+1/4x*sin2x+1/8cos2x+C