Nguyen Tien Dung, Three synthetic proofs of the Butterfly Theorem,
Forum Geometricorum, 17 (2017) 355--358.
Abstract. We give three synthetic proofs of the butterfly theorem, using Thales' theorem, the notions of isogonal conjugates, and spiral similarity respectively.
[ps file] [pdf]
Return to Forum Geom., 17 (2017) Table of Contents