原式=∫x(1+cos2x)/2 dx
=1/2∫xdx+1/2∫xcos2x dx
=x²/4+1/4∫xcos2x d2x
=x²/4+1/4∫xdsin2x
=x²/4+1/4xsin2x-1/4∫sin2xdx
=x²/4+1/4xsin2x+1/8cos2x+C