∫arctanxdx =xarctanx-1/2*ln(x^2+1)+C
分部积分法+凑微分法求解
∫arctanxdx =xarctanx-∫xdarctanx = xarctanx-∫x/(1+x²)dx
=xarctanx-(1/2)∫1/(1+x²)d(1+x²) = xarctanx-(1/2)ln(1+x²)+C