1. 9.8 Using the Sum and Difference Formulas
Rita Korsunsky

2. Formula for cos(α±β) Distance formula:
Let A and B be points on the unit circle. Then these are congruent triangles:
Distance formula:

3. Formula for cos(α±β)

4. Formula for sin(α±β)
Since
and

5. Sin = Sign

6. Deriving the Tan Sum Formula
Given:

7. The Tan Difference Formula
For the formula of tan(α±β), replace β with -β .

8. Example #1
Find the exact value of sin15°

9. Example #2
Find the exact value of:

10. Example #3 II I

11. Example #4
Show that

12. Example #5

13. Example #6

14. Example #7

15. Example #8

16. Example #8
Substitute α.
Split the fraction.