How to solve a recurrence relation using the back-substitution technique.
From University of Victoria: http://www.math.uvic.ca/faculty/gmacgill/guide/recurrences.pdf
From University of Idaho: http://www.cs.duke.edu/~reif/courses/alglectures/skiena.lectures/lecture3.pdf
From wikiHow: http://www.wikihow.com/Solve-Recurrence-Relations (take this one with a grain of salt...)