MathDB

30

Part of 1979 IMO Longlists

Problems(1)

Axes of symmetry intersect at angle.

Source: ILL 1979-30

6/2/2011
Let MM be a set of points in a plane with at least two elements. Prove that if MM has two axes of symmetry g1g_1 and g2g_2 intersecting at an angle α=qπ\alpha = q\pi, where qq is irrational, then MM must be infinite.
symmetrygeometrygeometric transformationreflectionrotationinvariantgeometry unsolved