1. What is coming up due?

2. Sum and Difference of Cosine
Section 5.3

3. Cosine of a Sum or Difference:
cos (A + B) = cos A cos B – sin A sin B cos (A – B) = cos A cos B + sin A sin B cos (A  B) = cos A cos B sin A sin B 

4. Ex: Rewrite using the cosine sum/difference formula
cos (90 – x)

5. Ex: Find the exact value
a. cos 75

6. b. cos 7/12

7. c. cos 40 cos 50 – sin 40 sin 50

8. Cofunction Identities

9. Ex: Write in terms of the cofunction.
tan 87
cos /12

10. c. csc (-1424) d. cot 

11. Ex: Use an identity to fill in the blank.
_______ 33 = sin 57
cos 70 = 1/_______20

12. Ex: Find .
a. tan  = cot (45º + 2) b. sec  = csc(/2 + 20º)

13. Ex: Rewrite as functions of .
a. cos(0º –  ) b. cos (180º +  )

14. Ex: Find cos (s + t) and cos (s – t)
a. cos s = -1/5 and sin t = 3/5 , s and t in QII

16. b. sin s = 3/5 and sin t = -12/13 , s in QI and t in QIII

18. Ex: True or False?
a. cos 42º = cos (30 º+ 12º) b. cos 74º = cos 60º cos 14º + sin 60º sin 14º c. cos /3 = cos /12 cos /4 – sin /12 sin /4