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Finding Derivatives Using Taylor/Maclaurin Polynomials

  1. Mar 12, 2010 #1
    1. The problem statement, all variables and given/known data

    Compute the 6th derivative of f(x) = arctan((x^2)/4) at x = 0. Hint: Use the Maclaurin series for f(x).

    2. Relevant equations

    The maclaurin series of arctanx which is ((-1)^n)*x^(2n+1)/2n+1

    3. The attempt at a solution

    I subbed in x^2/4 for x into the maclaurin series and got *summation* ((-1)^n)*x^(4n+2)/(4^2n+1)(2n+1). After that, i'm not sure what to do. I know that the 6th derivative in a general maclaurin series would be represented by *the 6th derivative of f at 0*/n! and x is to the power of 6. My prof said to find the value where the exponent of x in the series is 6.

    Any help would be greatly appreciated. Thanks!
     
  2. jcsd
  3. Mar 12, 2010 #2

    HallsofIvy

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    Okay, so you know that the general term is [itex]((-1)^n)*x^{4n+2}/(4^{2n+1})(2n+1)[/itex].
    And you know that the coefficient is the nth derivative over n!. Okay. For what n is
    4n+2= 6? What is the coefficient of [itex]x^6[/itex]?
     
  4. Mar 12, 2010 #3
    Yes, I did as such and found n = 1 to get x^6. Thus, the coefficient of x would be -(1/192), no? Apparently, the answer was wrong.
     
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