Circles (A61a) and (A61b): Dao pair

Definition

Let E and F be the midpoints of (O1) and (O2) respectively. Then let A61a be the point of intersection of BE and (O1), and A61b the point of intersection of AF and (O2). Let G of be the point of intersection of O1F and O2E. The circles centered at A61a and A61b passing through G are Archimedean. [Dao Thanh Oai, june 2014]
Source: A. Bogomolny, Dao's Archimedean Twins from Interactive Mathematics Miscellany and Puzzles http://www.cut-the-knot.org/m/Geometry/DaosTwins.shtml


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