Question

What is the formula of Circumcircle of a triangle and its radius?

Answer

Circumcircle of a triangle and its radius: $\left(\mathrm{i}\right)R=\frac{a}{2\sin A}=\frac{b}{2\sin B}=\frac{\mathrm{c}}{2\sin C}$
$\left(\mathrm{ii}\right)R=\frac{abc}{4△}$
$\left(\mathrm{iii}\right)R=\frac{\sin A}{a}=\frac{\sin B}{b}=\frac{\mathrm{Sin}C}{c}=\frac{1}{2R}$