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Compound Angles – sin(A+B) = cosAsinB+sinAcosB

February 7th, 2009 admin Leave a comment Go to comments

Compound angles are angles made by adding two other angles together. When using trigonometry unfortunately you cant just “times out” the trig function but have to use an identity. This post will consider how we get the identity for sin(A+B):

sin(A+B) = sinAcosB+sinBcosA

Compound angle of A+B showing how they relate

Compound angle of A+B showing how they relate

From the definition of sin=opp/hyp we find

sin(A+B) = RT/OR

But sinceRT comprises of RS+ST

Compund Angle derivation

By David Woodford

  1. March 1st, 2009 at 11:43 | #1

    Just passing by.Btw, your website have great content!

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  2. Dakaa
    March 11th, 2009 at 06:21 | #2

    lol, right timing, published this guide on the day i learned it, and i didn’t get it at all.

  3. Barry
    December 12th, 2009 at 13:42 | #3

    First class site

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