Do on your own: 

	13.1 #6, 29, 41
	13.2 all core problems
	13.3 all core problems

Hand in:

1.	13.2 problem 33
	
2.	A tetrahedron is a solid with 4 vertices and 4 triangular faces
	as shown in the Figure on page 858.  A regular tetrahedron is
	one where all 6 edges have the same length.

	(a) Find four points in three-space that are the vertices of a
	regular tetrahedron.  (It should go without saying: justify that
	these points are indeed vertices of a regular tetrahedron.)

	(b) Use vectors to compute the angles between edges.  In this and
	future problems, if you compute a decimal approximation to a
	quantity, you should also give an exact description.

	(c) Labeling the vertices P, Q, R and S, what is the angle 
	between PS and the median PM of the face PQR?  

	(d) Find a point O such that the vectors OP, OQ, OR and OS
	sum to zero.  In general, given any finite collection of
	points P1, P2, ..., Pk, how can you find a point O such
	that the vectors O P1, ... , O Pk sum to zero?