(x^2-xy+y^2)-(x+y-1)=[(x^2-2xy+y^2)+(x^2-2x+1)+(y^2-2y+1)]/2=[(x-y)^2+(x-1)^2+(y-1)^2]/2>=0,当x-y=x-1=y-1,即x=y=1时取等号.所以应是不小于.