y=(1-cosx)/sinxy'=[(1-cosx)'sinx-(1-cosx)(sinx)'] / sin^2x =(sin^2x+cos^2x-cosx) / sin^2x =(1-cosx) / sin^2x =(1-cosx) / (1-cos^2x) =(1-cosx) / (1-cosx)(1+cosx) =1 / (1+cosx)有不懂欢迎追问...