Trig Sum and Difference Identities

Youtube videos by Julie Harland are organized at http://YourMathGal.com
Uses the formula for the cosine of the sum of two angles to derive the formulas for the cosine of the difference of two angles, the sine of the sum of two angles, and the sine of the difference of two angles. Examples using the formula are provided. Aligned to CCSS: HSF-TF.9 . For more great math videos visit: www.youtube.com/user/videosbyjulieharland/videos