Diagonals yield isosceles triangles
Source: 43rd International Tournament of Towns, Junior O-Level P4, Fall 2021
February 18, 2023
geometryTournament of Townspolygon
Problem Statement
A convex -gon with is such that if a diagonal cuts a triangle from it then this triangle is isosceles. Prove that there are at least 2 equal sides among any 4 sides of the -gon.Maxim Didin