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