x^2+y^2-xy+2x-y+1=0x^2+2x+1-y(x+1)+y^2=0(x+1)^2-y(x+1)+y^2=0(x+1-y/2)^2+3y^2/4=0 则y=0,x+1-y/2=0,x=-1即x=-1,y=0
