MathDB

line of symmetry and every red point is reflected

Source: China TST 1994, problem 3

May 17, 2005

symmetrygeometrygeometric transformationreflectiontrapezoidcombinatorics unsolvedcombinatorics

Problem Statement

Find the smallest

n \in \mathbb{N}

such that if any 5 vertices of a regular

n

-gon are colored red, there exists a line of symmetry

l

of the

n

-gon such that every red point is reflected across

l

to a non-red point.