3x2+y2=163 x^{2}+y^{2}=163x2+y2=16
3x2+y2=113 x^{2}+y^{2}=113x2+y2=11
x2+y2=9x^{2}+y^{2}=9x2+y2=9
x2+9y2=25x^{2}+9 y^{2}=25x2+9y2=25
x2+4y2=4x^{2}+4 y^{2}=4x2+4y2=4
