2n+1 2n-1是奇数 (y-x)^(2n-1) = -(x-y)^(2n-1)
4n是偶数 (-x+y)^(4n) = (x-y)^4n
数字部分是7/10
后面那一大坨是:-(x-y)^[(2n+1)+(2n-1)+4n]=-(x-y)^8n
答案就是:-7/10(x-y)^8n