Math Medics
S.o.s. Math: Product and Sum Formulas
This math lesson lists the product and sum formulas, and gives detailed example of using them to solve algebraic trigonometry problems.
Other
Brown Math: Remembering Trig Identities
Faced with a large number of trigonometric identities, students tend to try to memorize them all. This site the emphasis is on understanding how the functions work and on memorizing only about a half dozen of them - all the others work...
Analyze Math
Analyze Math: Trigonometry: Product Sum and Sum Product Formulas
Learners explore trigonometric formulas. Definitions of the sum to product and product to sum formulas are included.