∫(1/(cosx+sinx)^2)dx＝∫1/(1+sin2x)dx (用万能代换）＝∫1/[1+2tanx/(1+tan^2x)]dx＝∫(1+tan^2x)/[(1+tan^2x)+2tanx]dx＝∫sec^2x/(1+tanx)^2dx＝∫1/(1+tanx)^2dtanx＝∫1/(1+tanx)^2d(1+tanx)＝-/(1+tanx)+C...
