(x-y)的9次方/(y-x)的8次方+(-x-y)的3次方/(x+y)的平方
=(x-y)的9次方/[(-1)的8次方×(x-y)的8次方]+[(-1)³×(x+y)³/(x+y)²
=(x-y)的9次方/(x-y)的8次方-(x+y)³/(x+y)²
=(x-y)的(9-8)次方-(x+y)的(3-2)次方
=(x-y)的1次方-(x+y)的1次方
=x-y-(x+y)
=x-y-x-y
=-2y