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Taylor series for tanh

  1. Mar 19, 2009 #1
    Hi.

    How can I derive the Taylor series expansion and the radius of convergence for hyperbolic tangent tanh(x) around the point x=0.

    I can find the expression for the above in various sites, but the proof is'nt discussed. I guess the above question reduces to how can I get the expression for the n^th order derivative of tanh(x) in terms of Bernoulli numbers.

    Many thanks in advance.
    joel.
     
  2. jcsd
  3. Mar 19, 2009 #2

    mathman

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    The radius of convergence for tanh is the same as it is for tan, which is pi/2.
     
  4. Mar 20, 2009 #3
    Thanks. But my questions are (a) How can I derive (not just the expression) the n^{th} coefficient of the Taylor series for tanh(x) around x=0, and (b) the derivation of the radius of convergence (by e.g. root test).
     
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