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

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

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

【1×（-4）-4+80】/（1+8-4+4)
=72/9
=8