题目

先化简,再求值：x²-y²-4+4y分之x²+y²-4-2xy,其中x=-1,y=2

提问时间：2020-10-10

答案

原式=[(x-y)²-4]/[x²-(y²-4y+4)]
=(x-y+2)(x-y-2)/(x²-(y-2)²)
=(x-y+2)(x-y-2)/(x+y-2)(x-y+2)
=(x-y-2)/(x+y-2)
=(-5)/(-1)
=5