Equation of Circle center Origin

Theorem
The equation of a circle with radius $R$ whose center is at the origin expressed in Cartesian coordinates is:


 * $x^2 + y^2 = R^2$

Proof
From Equation of Circle: Cartesian, the equation of a circle with radius $R$ and center $\left({a, b}\right)$ expressed in Cartesian coordinates is:


 * $\left({x - a}\right)^2 + \left({y - b}\right)^2 = R^2$

Setting $a = b = 0$ yields the result.