先化简,再求值,[(xy+2)(xy-2)-2(x^2y^2-2)]除xy,其中x=1,y=-2

问题描述:

先化简,再求值,[(xy+2)(xy-2)-2(x^2y^2-2)]除xy,其中x=1,y=-2

[(xy+2)(xy-2)-2(x^2y^2-2)]除xy
=(x²y²-4-2x²y²+4)÷xy
=-x²y²÷xy
=-xy
当x=1,y=-2时
原式=2