（x-y）的2n+1次方-（x-z）（x-y）的2n次方+2（y-x）的2n次方（y-z)
=(x-y)的2n次方[(x-y)-(x-z)+2(y-z)]
=(x-y)的2n次方(x-y-x+z+2y-2z)
=(x-y)的2n次方(y-z)