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 * Aim: How do we find the value of trigonometric functions of double angles?** //(These formulas will be on the Regents Reference sheet)//

By the end of the lesson, you will be able to...
 * 1) apply the formulas for sin (A+B), cos (A+B), and tan (A+B) to discover the formulas for sin(2x), cos(2x), and tan(2x)
 * 2) verify the validity of the formulas for the sine, cosine, and tangent of the angle 2x
 * 3) apply the formulas for sin (2x), cos (2x), and tan (2x) to find the exact value of expressions involving angles measured in radians and degrees
 * 4) state the double-angle formulas in words

For the first video, copy down the following into your notebooks and answer them whil watching the video. 1. What is the formula for sin (2x)? 2. What is the formula for cos (2x)? 3. Using the same strategy, develop the formula for tan (2x). Do this after you watch the video

[|Video 1]

For the second video, copy down these questions into your notebooks. Answer these as you watch this video
 * 1) What are the other cos(2A) formulas?
 * 2) How did the instructor derive these other formulas?
 * 3) Use this video to check your work for tan(2A).

[|Video 2]

This video will show you how to use a problem to find different answers not just double angles. **Ignore the last example with half angle formulas. Just watch what the instructor does with sum or difference and the double angle**.

[|Video 3]

Answers: a. -4/3, b. -3/4, c. sqrt7/4, d. -3sqrt7/8, e. 1/8, f. - 3sqrt7
 * **Classwork:** if tan a = -sqrt7/3 and lies in the second quadrant, find: a. **sec a**, b. **cos a**, c. **sin a**, d. **sin(2a)**, e. **cos(2a)**, f. **tan(2a)**


 * **Homework:** Complete 3-24 in multiples of 3

[|Double_Angles.JPG]


 * **Answers:**


 * [|A-Double_Angles.JPG]**


 * **Journal entry:** Explain why sin(2A) is not equal to 2sinA