化简求值:[(x+y)(x-y)-(x-y)²+2y(x-y)]÷4y,其中x=二分之一,y=2

题目

化简求值:[(x+y)(x-y)-(x-y)²+2y(x-y)]÷4y,其中x=二分之一,y=2

答案

[(x+y)(x-y)-(x-y)²+2y(x-y)]÷4y=[(x-y)(x+y-x+y)+2y(x-y)]÷4y=[(x-y)2y+2y(x-y)]÷4y=[(x-y)4y]/4y=(x-y) =(1/2-2)=-3/2