Question

|x-y+1|与（x+y-2010）的平方互为相反数,求（x+y)(x-y)的值?

Answer 1

|x-y+1|非负

（x+y-2010）的平方非负

两个非负的数互为相反数,只可能有：

x-y+1 = 0

x+y-2010 = 0

变形得

X - Y = -1

X + Y = 2010

因此

（x+y)(x-y)

= 2010×（-1）

= -2010