x2+y2+3x+4y=0x^{2}+y^{2}+3 x+4 y=0x2+y2+3x+4y=0
x2+y2+6x+8y=0x^{2}+y^{2}+6 x+8 y=0x2+y2+6x+8y=0
x2+y2−3x−3y=0x^{2}+y^{2}-3 x-3 y=0x2+y2−3x−3y=0
x2+y2−6x−6y=0x^{2}+y^{2}-6 x-6 y=0x2+y2−6x−6y=0