2x方+2y方-2xy-2x-2y+8
=x²-2xy+y²+x²-2x+1+y²-2y+1+6
=(x-y)²+(x-1)²+(y-1)²+6
当x=1,y=1时,代数式2x方+2y方-2xy-2x-2y+8有最小值,这个最值是6