Derive Cosine of a Sum Identity

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Taught by YourMathGal
  • Currently 4.0/5 Stars.
3003 views | 1 rating
Part of video series
Meets NCTM Standards:
Lesson Description:

This video shows the formula for deriving the cosine of a sum of two angles.

More free YouTube videos by Julie Harland are organized at http://yourmathgal.com

Questions answered by this video:
  • What is cos(A + B)?
  • What is the formula for cos(A + B)?
  • How can you derive the formula for the cosine of the sum of two angles using unit circle definitions, the pythagorean identity, and the distance formula?
  • Why does cos(A + B) = cosA*cosB - sinA*sinB?
  • What is the distance formula between two points?
  • What is the pythagorean trig identity?
  • Why does cos(A + B) not equal cosA + cosB?
  • Staff Review

    • Currently 4.0/5 Stars.
    This lesson will teach you about the cosine of the sum of two angles. You will also learn why the formula for breaking apart the cosine of the sum of two angles works. The proof of this identity is explained and proved in this video. All steps involved in the proof are explained and shown very clearly. The algebra done can get a little complicated, but it is very complete.