Three Planes in a Trihedron
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Start with a trihedron with apex and edges , , . Extend the edges by a factor to a trihedron , , . Then the planes , and are concurrent. The common point is shown in red.
Contributed by: Izidor Hafner (May 2017)
Open content licensed under CC BY-NC-SA
This problem was posed in [1, p. 220].
 V. V. Prasolov and I. F. Sharygin, Problems in Stereometry (in Russian), Moscow: Nauka, 1989.
"Three Planes in a Trihedron"
Wolfram Demonstrations Project
Published: May 5 2017