令： x = 1+t1 - x^m = 1 -(1+t)^m = -[mt + m(m-1)/2*t^2 + o(t^2)]1 - x^n = 1 -(1+t)^n = -[nt + n(n-1)/2*t^2 + o(t^2)]lim(m/1-x^m—n/1-x^n)=lim [m(1-x^n) - n(1-x^m)]/(1-x^m)(1-x^n)=lim{ -[mnt + mn(n-1...