1. Start with these formulas Subtract So we get

2. It’s the same with these other formulas

3. We call these Product to Sum Formulas Use these when you have a product of trig functions and you want a sum.

4. Sum To Product Formulas Let and This simplifies to

5. Likewise we have

6. These formulas are great for solving some trig equations By making a sum into a product we can use the zero property when we solve.

7. WHY do we have so many formulas??? Blame the physicists These formulas have proven to be Useful in simplifying and solving problems

8. You’ll need to know these formulas for the final exam By learning them now you will know they they are there later (to look up)