Geometric Artwork of Problem 812. Four Tangent Circles
and Area. iPad Apps

The figure above 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
. See also: Problem
812.