Whitman College: David Guichard's "Calculus, Chapter 8: Techniques of Integration, Section 8.1: Substitution"

Read Section 8.1 (pages 161-166). This section explains the process of taking the integral of slightly more complicated functions. We do so by implementing a "change of variables," or rewriting a complicated integral in terms of elementary functions that we already know how to integrate. Simply speaking, integration by substitution is merely the act of taking the chain rule in reverse.