Apollonius' Problem

Apollonius’ Problem is to compute the circle that is tangent to three given circles. There are up to eight such circles. In the interactive chart below, all circles are shown as simple single-stroke outlines. Drag the circles to reposition them, or use the sliders to change their diameters.

References:

1. https://observablehq.com/@d3/apollonius-problem
2. https://mathworld.wolfram.com/ApolloniusProblem.html