@article{amesa:/content/journal/10520/EJC-19eb008a40,
author = "Man, Yiu-Kwong",
title = "An elementary proof of Ptolemy’s theorem",
journal= "Learning and Teaching Mathematics",
year = "2019",
volume = "2019",
number = "27",
eid = "",
pages = "23-25",
doi = "",
url = "https://journals.co.za/content/journal/10520/EJC-19eb008a40",
publisher = "Association for Mathematics Education of South Africa (AMESA)",
issn = "1990-6811",
type = "Journal Article",
language = "English",
keywords = "",
abstract = "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).",
}