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问题: 求不定积分?

∫(tanx)^3dx

解答:

∫(tanx)^3dx
=∫tanx[(secx)^2-1]dx
=∫tanx(secx)^2dx -∫tanxdx
=∫tanxd(tanx) -∫sinx/cosxdx
=[(tanx)^2]/2 +-∫1/cosxd(xosx)
=[(tanx)^2]/2 +-ln|cosx|+C