Point and segment are given. Determine the locus of points in space which are vertices of right angles with one side passing through , and the other side intersecting segment .
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Point $A$ and segment $BC$ are given. Determine the locus of points in space which are vertices of right angles with one side passing through $A$, and the other side intersecting segment $BC$.
Izvor: Međunarodna matematička olimpijada, shortlist 1963
Školjka 
and segment 
are given. Determine the locus of points in space which are vertices of right angles with one side passing through