Question

已知2x－y＝－6，求代数式[（x的平方＋y的平方）－（x－y）的平方＋2y（x－y）]÷4y的值

Answer 1

[(x2+y2)-(x-y)2+2y(x-y)]÷4y
=[(x2+y2)-(x2-2xy+y2)+(2xy-2y2)]÷4y
=[x2+y2-x2+2xy-y2+2xy+2y2]÷4y
=(4xy+2y2)÷4y
=y(4x+2y)÷4y
=(2x+y)÷2
=-3

Answer 2

[（x的平方＋y的平方）－（x－y）的平方＋2y（x－y）]÷4y
=[x^2+y^2-(x^2-2xy+y^2)+2yx-2y^2]/(4y)
=(4xy-2y^2)/(4y)
=(2x-y)/2
=-6/2
=-3