# Proof: cos(a+b)=(cos a)(cos b)-(sin a)(sin b)

Using a similar method that he used to prove the sum of angles formula for sine, Sal shows the proof of the cosine sum of angles formula, cos (a+ b) = cos (a) cos (b) - sin (a) sin (b). This proof also uses the SOH-CAH-TOA model and some interesting geometric properties of parallel lines and angles.

Resource Details

10th - 12th
Subjects
Math
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Resource Types
Videos
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Audiences
For Teacher Use
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Instructional Strategy
Flipped Classroom
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Closed Captions
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Creative Commons
BY-NC-SA: 3.0