MathDB
Regular hexagon combo

Source: Polish MO Second round 2024 P4

February 10, 2024
combinatorics

Problem Statement

Let nn be a positive integer. A regular hexagon ABCDEFABCDEF with side length nn is partitioned into 6n26n^2 equilateral triangles with side length 11. The hexagon is covered by 3n23n^2 rhombuses with internal angles 6060^{\circ} and 120120^{\circ} such that each rhombus covers exactly two triangles and every triangle is covered by exactly one rhombus. Show that the diagonal ADAD divides in half exactly nn rhombuses.