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Homework Help: Straightforward differentiation, but think I have wrong sign somewhere

  1. Feb 18, 2009 #1
    1. The problem statement, all variables and given/known data, attempt at a solution

    Please see attached. I'm actually busy with a physics problem, but solving it requires that I complete this part correctly. It's straightforward differentiation, but I think I made an error with my signs somewhere and I can't for the life of me find where...

    Any pointers? (I believe this is going to be one of those *doh* situations :biggrin:)
    phyz
     

    Attached Files:

  2. jcsd
  3. Feb 18, 2009 #2

    Tom Mattson

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    Staff Emeritus
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    There's nothing wrong. The quantity in brackets in the last line is in fact zero. Don't forget:

    [tex]x\cdot x^{-7/2}=x^{1-7/2}=x^{-5/2}[/tex]
     
  4. Feb 18, 2009 #3
    You see...*DOH!* :biggrin:

    Thanks for the help! :smile:
     
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