Five proofs of an area characterization of rectangles - Martin Josefsson There are a handful of well known characterizations of rectangles, most...
Bicentric quadrilaterals through inversion - Albrecht Hess We show that inversion is a delightful tool for making some recent and some older...
A triad of circles tangent internally to the nine-point circle - Nikolaos Dergiades and Alexei Myakishev Given an acute triangle, we construct...
Soddyian triangles - Frank M. Jackson A Soddyian triangle is a triangle whose outer Soddy circle has degenerated into a straight line. This paper...
The butterfly theorem revisited - Nikolas Dergiades and Sung Hyun Lim We start with a proof of the original butterfly theorem, give without proof...
On tripolars and parabolas - Paris Pamfilos Starting with an analysis of the configuration of chords of contact points with two lines, defined on...
An elementary view on Gromov hyperbolic spaces - Wladimir G. Boskoff, Lucy H. Odom and Bogdan D. Suceava In the most recent decades, metric...
Generalizing orthocorrespondence - Manfred Evers B. Gibert [Forum Geom., 3 (2003) 21--27] investigates a transformation P→ P┴ of the plane of a...
Using complex weighted centroids to create homothetic polygons - Harold Reiter and Arthur Holshouser After first defining weighted centroids that...
Maximal area of a bicentric quadrilateral - Martin Josefsson We prove an inequality for the area of a bicentric quadrilateral in terms of the...
Improving upon a geometric inequality of third order - Toufik Mansour and Mark Shattuck We show that the best possible positive constant k in a...
Sherman's fourth side of a triangle - Paul Yiu We give two simple ruler-and-compass constructions of the line which, like the sidelines of the...
The spheres tangent externally to the tritangent spheres of a triangle - Floor van Lamoen We consider the tritangent circles of a triangle as the...
Finding integer-sided triangles with P^2 = nA - John F. Goehl A surprising property of certain parameters leads to algorithms for finding...
Non-Euclidean versions of some classical triangle inequalities - Dragutin Svrtan and Darko Veljan In this paper we recall with short proofs of...
Alhazen's circular billiard problem - Debdyuti Banerjee and Nikolaos Dergiades In this paper we give two simple geometric constructions of two...
A highway from Heron to Brahmagupta - Albrecht Hess We give a simple derivation of Brahmagupta's area formula for a cyclic quadrilateral from...
The perpendicular bisector construction, isotopic point and Simson line - Olga Radko and Emmanuel Tsukerman Given a noncyclic quadrilateral, we...
Harmonic conjugate circles relative to a triangle - Nikolaos Dergiades We use the term harmonic conjugate conics, for the conics C, C* with...
Some properties of the Newton-Gauss line - Catalin Barbu and Ion Patrascu We present some properties of the Newton-Gauss lines of the complete...
