x²+y²-4x-2y+5=0x^2-4x+4+y^2-2y+1=0(x-2)^2+(y-1)^2=0x-2=0 x=2y-1=0 y=1（√x）+y /（√x）-y=(√2+1)/(√2-1)=(√2+1)^2=3+2√2
