This is a pictorial derivation of the sine and cosine of the sum of two angles. It has helped us to understand the outcome by actually seeing the quantities in play. And, for our visual students, the concept is solidified.
We suggest that you use this as a handout to accompany your presentation in class.
The verbiage is parsimonius - but we offer some talking points in the Vocabulary section.
AA Geometric Derivation of the Trigonometric angle sum formulas by Orrin White is licensed under a Creative Commons Attribution 3.0 United States License