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Homework Help: Problem needing trig identities to find exact value

  1. May 20, 2012 #1
    1. The problem statement, all variables and given/known data
    Find the exact value of:

    sin (-5∏/12)


    2. The attempt at a solution

    sin (-45° + -30°) =

    sin -45° cos -30° + cos -45° sin -30° =

    (sqrt (2) / 2 )(sqrt (3) / 2 ) + (sqrt (2) / 2)(1 / 2) =

    (sqrt (6) + sqrt (2)) / 4



    However, the book has (-sqrt (6) - sqrt (2)) / 4 as the answer.
     
  2. jcsd
  3. May 20, 2012 #2

    tiny-tim

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    Welcome to pf!

    Hi Aaron! Welcome to pf! :smile:
    no, sin minus = minus sin :wink:
     
  4. May 20, 2012 #3
    Hmm, an exception. Thanks.
     
  5. May 20, 2012 #4

    NascentOxygen

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    Staff: Mentor

    S A
    T C


    No exceptions!
     
  6. May 21, 2012 #5

    tiny-tim

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    Aaron, look at the graph of sin ! :smile:

    (round the origin)

    alternatively, sin(0 - θ) = … ? :wink:
     
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