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Homework Help: Calculus quick question

  1. May 8, 2007 #1
    1. The problem statement, all variables and given/known data
    y = A cos (kx-wt)

    differentiate twice is -A^2k^2 cos (kx-wt)
    Why?

    2. Relevant equations
    n/a


    3. The attempt at a solution
    -w^2 A cos (kx-wt)
     
  2. jcsd
  3. May 8, 2007 #2

    Hootenanny

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    Apply the chain rule.
     
  4. May 8, 2007 #3
    Yes, you should use chain rule, but more importantly,what are you differentiating the function with respect to ? The answer the text gave has a quantity A^2, which I believe can't be obtained by differentiating the eqn, wrt any given variable in the function. Please check if you made an errors in copying the answer.
     
  5. May 8, 2007 #4

    Hootenanny

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    Good catch arunbg, didn't notice that myself :blushing:
     
  6. May 8, 2007 #5
    Well, on second thought , you can get the answer if you derive the function with respect to x/A treating A as constant (using good old chain rule), but then that would be calculus, not physics :wink:

    Oh, and hoot congrats for goin gold, and keep up the good work.
     
  7. May 8, 2007 #6

    Hootenanny

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    Thanks arunbg :smile:, much appreciated. I've not 'seen' you much on the forums lately, hope everything is good at your end.
     
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