A method for converting a three-dimensional coordinate system to a two-dimensional coordinate system is explained. (MN)

A class of triangles related to the Pythagorean triangles is described; theorems concerning this class are proved. (SD)

All lines which bisect the area of a triangle envelope a three-cusped curve made up of three hyperbolic arcs. (MM)

The first of three articles showing how inductively-obtained results in transformation geometry may be organized into a deductive system. This article discusses two approaches to enlargement (dilatation), one using coordinates and the other using synthetic methods. (MM)

Worksheets are provided for use by students in grades 8 and above when sectioning a tetrahedron. Lesson objectives include the discovery of generalizations regarding the cross-sections of a tetrahedron. (MK)

Investigates the idea of the center of mass of a polygon and illustrates centroids of polygons. Connects physics, mathematics, and technology to produces results that serve to generalize the notion of centroid to polygons other than triangles. (KHR)

Presents a simple proof of the Pythagorean Theorem that only requires prior knowledge of elementary properties of triangles. (MKR)

Summarizes and extends a well-known geometry theorem that states that any triangle inscribed in a circle with one side of the triangle a diameter of the circle, is a right triangle. (ASK)

A look at geometric angles. (MM)

This paper explores a geometrical way to sketch graphs of the general quadratic in two variables with Geometer's Sketchpad. To do this, a geometric procedure as described by De Temple is used, bearing in mind that this general quadratic equation (1) represents all the possible conics (conics sections), and the fact that five points (no three of…