EducationalYou could always buy used books from amazon or your local half priced books but many times the books are out of copyright and can be obtained free. Even if they're not, there are many free online textbooks created by volunteers that are just as effective. When the open courseware lectures tell you to do a homework from a textbook you don't have, search for the topic currently being discussed in the free textbook and work out all the practice problems you can.
Visit: Textbook Revolution: Free Non-Copyright Textbooks OnlineP2P networks such as Emule / Frostwire and torrent trackers such as Mininova and Ebook Share often host ebooks and online audio books. Some are out of copyright, but some are blatantly illegally redistributed, so beware. Try using Google Books to confirm a copyright).
