MathDB

Five rays in space

Source: Vietnam NMO 1987 Problem 6

February 4, 2009

geometry3D geometryspherevectoranalytic geometrypyramidgeometry unsolved

Problem Statement

Prove that among any five distinct rays

Ox

Oy

Oz

Ot

Or

in space there exist two which form an angle less than or equal to

90^{\circ}