因为|x+2y+1|>=0,(2x-y-2)²>=0
所以要使式子的值等于0,必须有
x+2y+1=0,2x-y-2=0
所以x+2y=-1,2x-y=2
(2x-y)²-2(2x-y)(x+2y)+(x+2y)²
=[(2x-y)-(x+2y)]²
=(2-(-1))²
=3²
=9