原式=∫[1-(cosx)^2]^2/(cosx)^2dx
=∫[(secx)^2-2+(cosx)^2]dx
=∫(secx)^2dx-2x+(1/2)∫(1+cos2x)dx
=tanx-2x+x/2+(sin2x)/4+C
=tanx-3x/2+(sin2x)/4+C.