Online Geometry Problem 812: Four Tangent Circles, Common Tangent Line,
Diameter, Area, Collinear Centers. Level: High School,
SAT Prep, College,
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 .