∵|x|=x,|y|=-y
∴x≥0,y≤0
∴x≥y
x+y≥0,|x+y|=x+y
∴|x|-|y|-|x+y|=x-(-y)-(x+y)=x+y-x-y=0
O(∩_∩)O哈哈~2分又到手了···