# Typography of Geometry Problem 812: Four Tangent Circles, Common Tangent Line, Diameter, Area, Collinear Centers, iPad Apps

### Proposition

The figure below shows the tangent circles
of diameters AB, BC, CD, and AD so that the line EFG is the common
tangent to circles AB, BC, and CD at E, F, and G, respectively. If EF =
a and FG = b, prove that the shaded area .

### Geometric Art using iPad or Mobile Apps

Geometric art is a form of art based on the use and application of geometric figures. A geometric figure is any set or combination of points, lines, surfaces and solids.

A mobile app or mobile application software is a computer program designed to run on smartphones and tablet computers.

See also:

Original problem
812.