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 Algebra Pre-Algebra and Basic Algebra Math Forum

 June 19th, 2011, 05:53 AM #1 Member   Joined: Dec 2009 Posts: 65 Thanks: 0 Polyhedra problem Hello! I don't understand the solution of this problem. Please, help me. Problem: Consider a polyhedra with 9 vertices, all of them having integer coordinates. Prove that there exists an other lattice point in the interior of the polyhedra. Solution: The points and are considered to belong to the same set, if is even, . In this way the set of lattice points is partitioned to 8 sets (??? why 8, and what are these sets ???), so there exists at least two points in the same set (it is clear, we use the pigeonhole principle). The midpoint of this segment determined by these points is also a lattice point because the coordinates of the midpoint are . Please help, many thanks, Crouch. June 19th, 2011, 11:33 AM #2 Senior Member   Joined: Feb 2010 Posts: 711 Thanks: 147 Re: Polyhedra problem The eight groups are based on the parity of the coordinates. E = even number, O = odd number. (E,E,E), (E,E,O), (E,O,E), (O,E,E) (O,O,O), (O,O,E), (O,E,O), (E,O,O) Since (E+E)/2 and (O+O)/2 are both integers, if two points lie in the same group then their midpoint must have integer values. Tags polyhedra, problem Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post mathLover Algebra 4 April 17th, 2012 02:02 AM Maurice Applied Math 0 January 30th, 2012 09:42 AM Algebra 7 November 21st, 2010 04:59 AM

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