x^2+4y^2=2x+4y-2
x^2+4y^2-2x-4y+2=0
(x^2-2x+1)+(4y^2-4y+1)=0
(x-1)^2+(2y-1)^2=0
x-1=0 2y-1=0
x=1 2y=1
x-2y=0
x-2y的平方根=0