Researchers find history in the diagrams of Euclid’s

Abstract

The fourth book of Euclid’s Elements, a 2,300-year-old geometry text, includes directions for constructing a 15-sided polygon inside a circle. The first step is familiar to geometry students: Draw an equilateral triangle and a regular pentagon so their vertices touch the circle and the two shapes share one vertex. In addition to text directions, the Elements included diagrams that illustrated the method.