An equilateral triangle divided into 81 triangles.
Source: St. Petersburg MO 2000, 11th grade, P1
April 22, 2023
geometrycongruent trianglesparallelogram
Problem Statement
An equilateral triangle with side length 9 is divided into 81 congruent triangles with segments which are parallel to the sides of the triangle. Prove that it cannot be divided into more than 18 parallelograms with sides 1 and 2.[I]Proposed by O.Vanyushina