2013/04/16 by Marc Chamberland, Doron Zeilberger, Chamberland, Marc +1
Mathematics · #Combinatorics (math.CO) #FOS: Mathematics #math.CO
paper · pdf · doi:10.48550/arxiv.1304.4547
2 pages
arxiv created 2013/04/16 · arxiv updated 2013/04/17
We give a short proof of a Ptolemy-style result first discovered and proved by Jane McDougall. It may be viewed as a generalization to any even number of points of the cubic relation connecting the six joint distances of four points on a circle (whose quadratic relation is the famed Plucker relation, alias Ptolemy's theorem). This article is in fond memory of Andrei Zelevinsky (1953-2013) who loved Ptolemy's theorem.