Let be three rays, and a point inside the trihedron . Consider all planes passing through and cutting at points , respectively. How is the plane to be placed in order to yield a tetrahedron with minimal perimeter ?
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Let $Ox, Oy, Oz$ be three rays, and $G$ a point inside the trihedron $Oxyz$. Consider all planes passing through $G$ and cutting $Ox, Oy, Oz$ at points $A,B,C$, respectively. How is the plane to be placed in order to yield a tetrahedron $OABC$ with minimal perimeter ?
Izvor: Međunarodna matematička olimpijada, shortlist 1973
Školjka 
be three rays, and 
a point inside the trihedron 
. Consider all planes passing through 
, respectively. How is the plane to be placed in order to yield a tetrahedron 
with minimal perimeter ?