(2x-y)^2-2(2x-y)(2x+y)+(2x+y)^2
=（2x-y-2x-y)²
=4y²
|x+2y-1|+(2x-y-2)^2=0
所以x+2y-1=0
2x-y-2=0
所以x=1,y=0
所以原式=0