设0设0
设0sqrt(x^2+y^2-2xy+4x-4y+4)+sqrt(1-2x+x^2)-sqrt(y^2-4y+4)=sqrt(x-y+2)^2+sqrt(x-1)^2-sqrt(y-2)^2=x-y+2+1-x-(2-y)=x-y+2+1-x-2+y=1