再帮忙算一题初一代数题~~

来源：百度知道编辑：UC知道时间：2024/05/15 17:04:55

已知x-y=3,求代数式7-x+y-(y-x)^2(的平方)的值.

谢谢!!~

7-x+y-(y-x)^2
=7-(x-y)-(x-y)^2
=7-3-3^2
=7-3-9
=-5

-2

x-y=3=>(x-y)^2=9
7-x+y=7-(x-y)=4
故=-5
现在的初中生都会用网络了吗，真是神奇...

7-(x-y)-(x-y)^2=-5

原式=7-(x-y)-(x-y)^2=7-3-9=-5
要记住（a-b)^2=(b-a)^2