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Math Help - Infinite series problem

  1. #1
    Member Em Yeu Anh's Avatar
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    Red face Infinite series problem

    Find the radius of convergence and interval of convergence of the series

    \sum_{n=2}^{\infty}\frac{x^{2n}}{n(lnn)^2}
    Last edited by Em Yeu Anh; March 1st 2010 at 07:09 PM.
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  2. #2
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    What were your conculsions from the Ratio Test?
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  3. #3
    Member Em Yeu Anh's Avatar
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    Quote Originally Posted by TKHunny View Post
    What were your conculsions from the Ratio Test?
    \lim_{n\to\infty}|\frac{x^{2n+2}}{(n+1)(ln(n+1))^2  }*\frac{n(lnn)^2}{x^{2n}}|

    = \lim_{n\to\infty}|x^2(\frac{n}{n+1})\frac{(lnn)^2}  {(ln(n+1))^2}

    It's simplifying the natural logarithms that I am a bit confused with (hopefully I did not make an error yet) sorry, I should have specified that earlier.
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  4. #4
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    Well, that was the application of the Ratio Test.

    You did not make any conclusion.

    Why do you require simplification? Let's draw some conclusions without it. It looks to me like just about every piece is approaching unity. Where does that leave us?

    Note: Nice screen name. I wish more folks felt that way about mathematics! Why do you hoist a China flag and speak from Viet Nam?

    Other Note: From your experience, does whatever culture you know tell women and girls that they can't do math? Obviously, that would be a silly thing to tell you, but it may remain a common cultural message.
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