x2+y2−ax=0x^{2}+y^{2}-a x=0x2+y2−ax=0
x2+y2+ax=0x^{2}+y^{2}+a x=0x2+y2+ax=0
x2+y2+2x=0x^{2}+y^{2}+2 x=0x2+y2+2x=0
x2+y2−2x=0x^{2}+y^{2}-2 x=0x2+y2−2x=0