这种有理分式的不定积分并不难,只要按照步骤一步一步进行即可,具体步骤参见
http://202.113.29.3/nankaisource/mathhands/calculus/s0204/s020403/t02040301.htm
解答:∫(1-u)/(1+u^2)du=∫1/(1+u^2)du-∫u/(1+u^2)du=arctanu-(1/2)∫[1/(1+u^2)]d(1+u^2)=arctanu-(1/2)ln(1+u^2)+C