The 15o Problem

By Geoff Estes and Richard Moushegian

Problem Statement:

  • Inside a square ABDE, take a point C so that CDE is an isosceles triangle with angles 15oat D and E.  What kind of triangle is ABC?

History of the Problem:

  • This problem was an exercise that was found in the text Introduction to Geometry by Coxeter.  The exploration of the problem's solution was initially done in Geometer's Sketchpad (GSP).  Searching for other means of a solution, we tried other methods of approaching the problem, which led us to road blocks!  We have two ways to work this problem and are currently searching for other approaches.  Keep checking back for updates to this page.
    Geoff and Rich

Table of Contents

Geoff's Page | Rich's Page