# Equation of Sphere/Corollary

## Theorem

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

- $x^2 + y^2 + z^2 = R^2$

## Proof

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

- $\paren {x - a}^2 + \paren {y - b}^2 + \paren {z - c}^2 = R^2$

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

$\blacksquare$

## Sources

- 2008: Ian Stewart:
*Taming the Infinite*... (previous) ... (next): Chapter $6$: Curves and Coordinates