DIFFERENTIAL EQUATIONS AND BOUNDARY VALUE PROBLEMS by Edwards and Penney (Chapters 1-6).
MATLAB book: GETTING STARTED WITH MATLAB by Rudra Pratap (about $18) is recommended. If you did not learn MATLAB well enough (or at all) in CS100 then you may want to spend 3-5 hours slowly going through the tutorials in this book. MATLAB is useful for many courses so you might consider purchase of the STUDENT EDITION (about $60) for use on your own computer (about $2000) to help with school in general (about $100,000).