Euclid's Elements Book 1, Proposition 7

Project Euclid presents Euclid's Elements, Book 1, Proposition 7 "Given two straight lines constructed from the ends of a straight line and meeting in a point, there cannot be constructed from the ends of the same straight line, and on the same side of it, two other straight lines meeting in another point and equal to the former two respectively, namely each equal to that from the same end." Presented by Nancy Ko, St. John's College, Class of 2015