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Points in the space - IMO LongList 1992 SAF1

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September 2, 2010
geometryparallelogramprojectionIMO ShortlistIMO Longlist

Problem Statement

If A,B,CA, B, C, and DD are four distinct points in space, prove that there is a plane PP on which the orthogonal projections of A,B,CA, B, C, and DD form a parallelogram (possibly degenerate).
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