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Homework Help: Radius of convergence question

  1. Apr 1, 2012 #1
    1. The problem statement, all variables and given/known data
    Suppose that the following series converges when x = -4 and diverges when x = 6.
    ∑{n=0 -> ∞} c_n • x^n

    What is the interval of convergence?

    3. The attempt at a solution
    I think it is [-5,5) but my friend reckons that it is [-5,6). I don't think [-5,6) is correct because this interval would tell us that 5 is a point of convergence but we don't know that... Am I right?
  2. jcsd
  3. Apr 1, 2012 #2


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    You don't have enough information. All you know for sure is you have a radius of convergence at least 4 and not more than 6.
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