MathDB
vietnam 1999

Source:

August 20, 2003
trigonometryvectorgeometry solvedgeometry

Problem Statement

OA,OB,OC,OD OA, OB, OC, OD are 4 rays in space such that the angle between any two is the same. Show that for a variable ray OX, OX, the sum of the cosines of the angles XOA,XOB,XOC,XOD XOA, XOB, XOC, XOD is constant and the sum of the squares of the cosines is also constant.
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