1. Aim: How do we prove and apply the Pythagorean identities?
Do Now: Find the value of 1. 2. 3. 4.
HW: p.414 # 4,6,8,10,12,14,16,18,20,21

2. A point (x,y) is on the unit circle1
By the Pythagorean Theorem x2 + y2 = 12 = 1
Replace x and y by cosθ and sinθ, a new equation can be formed or

4. Ex. Use the identities to solve problems
We call those three identities as Pythagorean Identities since they are derived from Pythagorean Theorem.
Ex. Use the identities to solve problems
A in quad. II, find cos A
A in quad. II, then cos A = -.8

5. 1. 2. 3. , in III, find 4. in III, find A in quad. IV, find sin A
A in IV, find sec A 3. ,
in III, find 4.
in III, find

6. Simplify the following:5. 6. 7. 8. 9.
10.