In plane geometry, Morley's trisector theorem is a theorem which could have been discovered by the ancient Greek geometers, but apparently was not. It states that in any triangle, the three points of intersection of the adjacent angle trisectors form an equilateral triangle, called the Morley triangle. The theorem was discovered in 1899 by Anglo-American mathematician Frank Morley. It has various generalizations, in particular if all of the trisectors are intersected one obtains four other equilateral triangles.

External links

• Morley's theorem - Introduction with animation by Antonio Gutierrez from Geometry Step by Step from the Land of the Incas.
• Morley's Miracle Several proofs of Morley's theorem