Trigonometry

"The idea behind teaching is to expect students to learn why things are true, rather than have them memorize ways of solving a few problems, as most of our books have done. [This] same philosophy lies behind the current text by Gelfand and Shen. There are specific practical problems but there is much more development of the ideas....[The authors] have shown how to write a serious yet lively book on algebra."

--- R. Askey, The American Mathematics Monthly (review of Algebra)