Stage: 5 Challenge Level: 
Take a cube of side length one unit. A vertex of the cube and the centres of the three faces not containing that vertex form the vertices of a tetrahedron. What is the surface area of this tetrahedron?
Arcs, sectors and segments. Spheres. Surface and surface area. Cubes. Visualising. Coordinates - 3D. Pythagoras' theorem. Long problems. Rotations. Tetrahedra.
Published December 2000.
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