4

Part of 2022 Indonesia MO

Problems(1)

A particular case of an "unsolved" problem

Source: Indonesia National Math Olympiad 2022 Problem 4 (INAMO 2022/4)

Given a regular

26

-gon. Prove that for any

9

vertices of that regular

26

-gon, then there exists three vertices that forms an isosceles triangle.

combinatoricsIndonesiaIndonesia MO