MathDB
Least n such that n disks cover a set of points

Source:

October 4, 2010
Extremal combinatoricspoint setcombinatorial geometrygeometryIMO ShortlistIMO Longlist

Problem Statement

(SWE3)(SWE 3) Find the natural number nn with the following properties: (1)(1) Let S={P1,P2,}S = \{P_1, P_2, \cdots\} be an arbitrary finite set of points in the plane, and rjr_j the distance from PjP_j to the origin O.O. We assign to each PjP_j the closed disk DjD_j with center PjP_j and radius rjr_j. Then some nn of these disks contain all points of S.S. (2)(2) nn is the smallest integer with the above property.