The coordinates of any point (P) of a circle whose center coincides with the point of intersection of the axes (O) form a right triangle. By the Pythagorean theorem, the relationship x² + y² = R2 will always hold.

In 1936, the English chemist Frederick Soddy (Nobel Prize winner in chemistry in 1921) rediscovered the theorem, and published his version in the journal Nature. He also expands it to the case of five spheres tangent to each other (if you know English, you can look for the original on the Internet)