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

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

人气：152 ℃　时间：2019-08-20 21:46:33

解答

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