设un(x)=[(-1)^n/(2n+1)](x-1)^(2n+1)
则u(n+1)(x)=[(-1)^(n+1)/(2n+3)](x-1)^(2n+3)
因为ρ=lim|u(n+1)(x)/un(x)|=lim|(2n+1)/(2n+3)||x-1|^2=|x-1|^2
当ρ