(1)a-b=-2
3a+b-(b-a)^2+a-5b+2(a-b)^2
=4a-4b+(a-b)^2
=4(a-b)+(a-b)^2
=-8+4
=-4
(2)
2(x+y)-2/3(x-y）+1/4(x+y)+2/3(x-y)+2/3(x-y)
=9/4(x+y)+2/3(x-y)
=35/12x+19/12y
=-35/24-57/24
=-23/6第一題的第二步怎么沒有2(a-b)^2?合并了啊因?yàn)?b-a)^2=(a-b)^2啊.......這 .....怎么可以合并呢因?yàn)?b-a)^2=(a-b)^2-(b-a)^2+2(a-b)^2=-(a-b)^2+2(a-b)^2=(a-b)^2那第二題的第二步為什么是2/3(x-y)？-2/3(x-y)+2/3(x-y) +2/3(x-y)=2/3(x-y)呃 題目打錯(cuò)了.........應(yīng)該是 2(x+y)-2/3(x-y）+1/4(x+y)+2/3(x-y)2(x+y)-2/3(x-y）+1/4(x+y)+2/3(x-y)=2(x+y)+1/4(x+y) -2/3(x-y）+2/3(x-y)=9/4(x+y) =9/4*(-2)=-9/2希望能得到你的認(rèn)同啊