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Homework Help: Identity proof

  1. Oct 3, 2007 #1
    1. The problem statement, all variables and given/known data
    Prove the following product-to-sum identities:
    i) cosucosv = 1/2[cos(u + v)+cos(u - v)]

    ii) sinusinv = 1/2[cos(u - v) - cos(u + v)]

    Any help/hints would be appreciated. The TAs (teacher assistants) can't help us with our problem set questions, so I'm stuck on this one. I really suck at proving identities. :(
     
  2. jcsd
  3. Oct 3, 2007 #2

    Dick

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    You must have sum and difference formulas for cos(u+v) and cos(u-v), right? Use them.
     
  4. Oct 3, 2007 #3
    What do you mean by sum and difference formulas?
     
  5. Oct 3, 2007 #4

    Dick

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    cos(u+v)=cos(u)cos(v)-sin(u)sin(v). What's cos(u-v)?
     
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