Question Number 48984 by peter frank last updated on 30/Nov/18
Commented by mr W last updated on 01/Dec/18
$${director}\:{circle}\:{of}\:{a}\:{circle}\:{is} \\ $$$${x}^{\mathrm{2}} +{y}^{\mathrm{2}} =\left(\sqrt{\mathrm{2}}{a}\right)^{\mathrm{2}} \\ $$$${or} \\ $$$${x}^{\mathrm{2}} +{y}^{\mathrm{2}} =\mathrm{2}{a}^{\mathrm{2}} \\ $$