Problem : Using your knowledge of concentric circles come up with a definition for concentric spheres.
Problem : Which of the regular polyhedra are prisms?
Problem : Triangles can be combined to form any polygon. Is there a geometric solid that can be combined to form any of the regular polyhedra?
Problem : Based on your knowledge of plane geometry, develop definitions for polyhedra inscribed in a sphere and polyhedra circumscribed about a sphere.
Problem : Devise a definition of the center of a regular polyhedron.