x2+y2−4=0x^{2}+y^{2}-4=0x2+y2−4=0
x2+y2+4=0x^{2}+y^{2}+4=0x2+y2+4=0
x2+y2−1=0x^{2}+y^{2}-1=0x2+y2−1=0
x2+y2−2=0x^{2}+y^{2}-2=0x2+y2−2=0