y = (1+cosx)/(1-cosx)
dy = [ (1+cosx)/(1-cosx) ] ' dx
= [ (-sinx)*(1-cosx) - (1+cosx)*sinx ] / (1-cosx)^2 dx
= - 2sinx / (1-cosx)^2 dx
懂了请采纳o(∩_∩)o