Some Cosine Identity

Students will explore the identity of cos(A+B) in three different ways. First algebraically on the one unit circle, second a proof without words, and third by graphing. Note the proof without words images come from A. Bogomolny, Addition and Subtraction Formulas for Sine and Cosine from Interactive Mathematics Miscellany and Puzzles http://www.cut-the-knot.org/triangle/SinCosFormula.shtml, Accessed 02 October 2016

By Luke Walsh