4x^2+9y^2-4x+12y+5=0
4x^2-4x+1+9y^2+12y+4=0
(2x-1)^2+(3y+2)^2=0
x=1/2.y=-2/3
{(x,y)|x=1/2,y=-2/3}.
x^2表示x的平方.