（x-1)ⁿ﹢¹－x(x-1)ⁿ=1
(x-1)ⁿ [(x-1) -x] = 1
(x-1)ⁿ = - 1
n 为偶数时,无实数根
n 为奇数时,x-1 = -1,x = 0