%0 Journal Article
%A Man, Yiu-Kwong
%T An elementary proof of Ptolemy’s theorem
%D 2019
%J Learning and Teaching Mathematics,
%V 2019
%N 27
%P 23-25
%@ 1990-6811
%I Association for Mathematics Education of South Africa (AMESA),
%X IntroductionPtolemy’s theorem is a well-known result in plane geometry and can be stated as follows:*If ABCD is a cyclic quadrilateral with sides a, b, c, d and diagonals e, f, then ac +bd = ef*In this article we present an elementary proof of Ptolemy’s theorem based on basic trigonometry, circle geometry and transformation geometry. The proof is different to those described elsewhere – see for example Johnson (1929), Coxeter & Greitzer (1967), Ostermann & Wanner (2012) and Miculita (2017).
%G English,
%U https://journals.co.za/content/journal/10520/EJC-19eb008a40