答：
（x-y）的2N次方-（x-y）的2n+1次方+（y-x）的2n-1次方
=(x-y)^(2n)-(x-y)^(2n+1) - (x-y)^(2n-1)
=[ (x-y) -(x-y)^2-1 ] *(x-y)^(2n-1)
= - [ (x-y)^2-(x-y)+1 ] *(x-y)^(2n-1)