Question

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

Answer 1

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