Question

先化简 再求值:[4(xy-1)^2-(xy+2)(2-xy)]1/4xy,其中x=-2,y=1/5

Answer 1

[4(xy-1)^2-(xy+2)(2-xy)]1/4xy
=[4(xy-1)^2 +(xy+2)(xy-2)]1/4xy
=[4(xy)²-8(xy)+4+(xy)²-4]÷(4xy)
=[5(xy)²-8(xy)]÷(4xy)
=(5xy-8)/4
已知x=-2，y=1/5，那么：xy=-2/5
所以：原式=(5xy-8)/4=[5*(-2/5)-8]/4=(-10)/4=-5/2

Answer 2

:[4(xy-1)^2-(xy+2)(2-xy)]1/4xy
=(4x²y²-8xy+4-4+x²y²)×1/4xy
=5xy/4-2
当x=-2 y=1/5时
原式=-1/2-2=-5/2

Answer 3

（xy-1）2=x2y2+1-2xy。 （xy+ 2）（2-xy）=4-x2y2。 4x2y2+4-8xy-4+x2y2=5x2y2-8xy
xy（5xy-8）1\4xy=-5/2

我是在找题目的时候找到你这题的，有点晚。见谅