In addition to the two pairs of Archimedean circles associated with the arbelos
constructed by Dao Thanh Oai [1], we construct two more pairs. Given a segment
AB with an interior point C, consider the semicircles (O), (O1), (O2) with diameters
AB, AC, and CB, all on the same side of AB. The perpendicular to AB at
C intersects (O) at D. Let a and b be the radii of the semicircles (O1) and (O2)
respectively. The Archimedean circles have radii ab
a+b .