2015-2016 Spring OMO #23
Source:
March 29, 2016
Online Math Open
Problem Statement
be the set of all lattice points with . A subset is called BQ if it has the following properties:(a) contains at least three points, no three of which are collinear.
(b) One of the points in is .
(c) For any three distinct points , the orthocenter of is in .
(d) The convex hull of contains at least one horizontal line segment.Determine the number of BQ subsets of . Proposed by Vincent Huang