Proceedings of the Edinburgh Mathematical Society

Table of Contents - Volume 20 - 1901  

Research Article

History of a theorem in Elementary Geometry

J. S. Mackay

The theorem is

If the straight lines bisecting the angles at the base of a triangle and terminated by the opposite sides be equal, the triangle is isosceles.

This theorem was in the year 1840 communicated by Professor Lehmus of Berlin to Jacob Steiner with a request for a pure geometrical proof of it. The request was complied with at the time, but Steiner's proof was not published till some years later.