求不定积分∫1/[(x^2+1)]^2dx.

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求不定积分∫1/[(x^2+1)]^2dx.

求不定积分∫1/[(x^2+1)]^2dx.
求不定积分∫1/[(x^2+1)]^2dx.

求不定积分∫1/[(x^2+1)]^2dx.
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

令x=tant,则dx=(sect)^2dt,
∫1/[(x^2+1)]^2dx=∫(cost)^2dt=1/2×∫(1+cos(2t))dt=t/2+1/2×sintcost+C=1/2×arctanx+x/[2(1+x^2)]+C