Title: Draw three circles and find their tangent circles in C#
This example is similar to previous one Find circles that are tangent to three given circles (Apollonius' Problem) in C# except it lets you click and drag to draw the three given circles. It then finds the (up to) 8 tangent circles.
For more information see the previous example and the links it mentions.
Download the example to experiment with it and to see additional details.