IMO Shortlist 1966 problem 56
Dodao/la:
arhiva2. travnja 2012. In a tetrahedron, all three pairs of opposite (skew) edges are mutually perpendicular. Prove that the midpoints of the six edges of the tetrahedron lie on one sphere.
%V0
In a tetrahedron, all three pairs of opposite (skew) edges are mutually perpendicular. Prove that the midpoints of the six edges of the tetrahedron lie on one sphere.
Izvor: Međunarodna matematička olimpijada, shortlist 1966
Školjka 
