Online free references for algorithms
Data Structures and Algorithms book by Shaffer
http://people.cs.vt.edu/~shaffer/Book/C++3elatest.pdf
Master theorem proof is on pages 482 - 484
Cormen, et. al.
2nd edition
http://www.ebook3000.com/Introduction-to-Algorithms--SecondEdition_10793.html
Other books
http://www.freebookcentre.net/CompuScience/free-computer-algorithmbooks.html