分开积分=[1/(1+u^2)-u/(1+u^)]duarctanu-0.5ln(1+u^2)+C
∫(1-u)/(1+u^2)du=∫1/(1+u^2)du-∫u/(1+u^2)du=arctanu-1/2∫1/(1+u^2)du^2=arctanu-1/2ln(1+u^2)+C
