∫（cosx-sinx分之cosx）dx
=∫[(cos^2x+cosxsinx)/(cos^2x-sin^2x)]dx
=∫[(1/2+cos2x/2+sin2x/2)/cos2x]dx
=∫(sec2x/4)d2x+∫1/2dx+∫(sin2x/4)d2x
=1/4ln|sec2x+tan2x|+x/2-cosx/4+c