y=a/by'烂嫌=(a'b-ab')/(b^2)y=x/(1-cosx)y'凯历历＝x/(1-cosx)' =[x'(1-cosx)-x(1-cosx）]'/[(1-cosx)^2] = [(1-cosx)-xsinx ] /盯搜 [(1-cosx)^2]
y'＝ [x/1-cosx]' = [(1-cosx)-xsinx ] / (1-cosx)^2
g
