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Homework Help: Maclaurin Series

  1. Dec 9, 2008 #1
    1. The problem statement, all variables and given/known data

    (1 pt) Compute the 9th derivative of:
    f(x) = [tex]\frac{cos(6x^4)-1}{x^7}[/tex]
    at x=0.

    2. Relevant equations

    Hint: Use the MacLaurin series for f(x).

    3. The attempt at a solution

    I have tried many weird ways and cannot come up with the correct numerical answer. I've gotten 0 each time and it still comes up as wrong. Please help point me in the correct direction, even if it is only a verbal explanation!

    Thanks so much
  2. jcsd
  3. Dec 9, 2008 #2


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    Science Advisor
    Homework Helper

    The only term in the expansion that would contribute to a 9th derivative would be the term containing x^9. If you look up the Maclaurin series of cos you'll it can be written as a sum of even powers of it's argument. The fourth power of 6x^4 contains an x^16. 16-7=9. Is that enough of a hint.
  4. Dec 9, 2008 #3
    Yes, thank you very much. I think I can work it out now!
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