(a) Let A,B,C be points in R^3 with coordinates (1,0,0), (0,1,0) and (0,0,1) respectively. Find the coordinates of D so that ABCD is a regular tetrahedron (ie a tetrahedron with all sides of equal length).
(b) Find cos(phi) where phi is the dihedral angle of ABCD. Hint: If E is the midpoint of AB, then phi is the angle of ED, EC. Hint: cos(phi) is a small positive rational number with numerator 1.
Prove by induction that if more than n bees visit n hives, then there exists a hive that is visited by more than one bee.