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 * Aim: How do we apply double-angle formulas to solve trigonometric equations?**

At the end of this lesson, you will be able to...
 * 1) state the trigonometric formulas involving double angles
 * 2) describe which double angle formula is needed to solve a trigonometric equation
 * 3) solve trigonometric equations using double angle formulas
 * 4) express solutions to the required degree of accuracy in the specified interval

OK, this lesson does not involve any videos. (I'm sure you're happy about that :) ). All you need to do is to substitute the double-angle function for it's equivalent and then solve like you did in previous lessons.


 * Classwork:**
 * 1) Find to the nearest degree the roots of cos2x - 2 cosx = 0 from 0__<__x<360. (Ans: 111 degrees or 249 degrees)
 * 2) Find the values for x if sin2x - sinx = 0 on the interval 0__<__x<2 pi (Ans: 0, pi, pi/3, 5pi/3)


 * Homework:** Complete 3-19 odd

[|Double_angle_app.JPG]


 * Answers:**

[|A-Double_Angle_App.JPG]


 * Journal entry:** Since there are three expansion formulas for y = 2cosa, how do you decide which formula substitution is best to use when using a trig equation containing cos 2a?