1. The Inverse Cosine Function Lesson 5.3

2. Reminder… y = cos x

3. y = cos -1 x If we took y = cos x on its entire domain, the inverse would not be a function So, we restrict the domain of cos -1 x to 0 ≤ y≤ π Different calculators  cos -1 x = arccos = acos

4. Reminder… y = cos x

6. Example 1 Evaluate arccos (1/2), giving an answer in radians. arccos(1/2) = x cos x = ½ (between 0 and π) x = 60˚ So π/3

7. Example 2 Find the exact value of cos -1 Cos x = (between 0 and π) x = 135˚ or 3π/4

8. Example 3 Evaluate cos -1 (.9925341) to the nearest degree. x = 7˚

9. Example 4 Find the cos (cos -1 (1/2)) cos (60) 1/2 Find the cos -1 (cos(-30˚)) cos -1 ( ) 30

10. Homework Pages 325 – 326 4 – 12, 15, 16 (skip 4 a and b)