求不定积分∫1/[(x^2+1)]^2dx.

Answer 1

换元法
令x=tany
则∫1/[(x^2+1)]^2dx=∫1/secy^4dtany=∫1/secy^2dy=∫cosy^2dy
==∫(cos2y+1)/2dy=y/2-sin2y/4+c
y=arctanx
所以原式=arctanx/2-sin(2arctanx)/4+c