Reading Assignment: 
   Sections 3.6 and 3.7.  We covered 3.6 today, and will cover
   3.7 on Monday.

When reading ...
   Can you, after reading the account in 3.7 of how they get 
   the formula involving the Wronskian, close your book, and
   derive the formula yourself?

Problems:
   Section 3.6 : 1,2,3,14,15,17, 20a, 22a

      Note:  in 20a, 22a: write down your guess, and check 
      it against the homogeneous solutions (eg, if we want a 
      particular solution to Ly = 5e^(3t), and e^(3t) is a solution 
      of Ly = 0, then
                 y_p = Ae^(3t)
      is not a decent guess.  Rahter, in this case you should try 
                 y_p = Ate^(3t)