Archimedes called this shape the arbelos, a shoemaker's knife: a big half circle with two smaller ones cut out of it, meeting at C. Its area is hard to guess, so he found a circle with exactly the same area: the one whose diameter is the line from C up to the big arc.
The source code is at github.com/KirillOsenkov/LiveGeometry. It is written in .NET and Avalonia.