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Simple? maclaurin series (1-x)^-2

  1. Dec 4, 2012 #1
    1. The problem statement, all variables and given/known data
    what is the maclaurin series expansion of the function (1-x)^-2


    2. Relevant equations
    maclaurin series


    3. The attempt at a solution
    part of the solution is to find the n derivatives of the function to setup the series
    MY ANSWERS
    n fn(x)
    0 (1-x)^-2 this should be the 0th derivative of the function
    1 -2(1-x)^-3 this should be the first derivative of the function
    2 6(1-x)^-4 second derivative
    3 -24(1-x)^-5 third derivative
    TEXTBOOK ANSWERS
    n fn(x)
    0 (1-x)^-2 this should be the 0th derivative of the function
    1 2(1-x)^-3 this should be the first derivative of the function
    2 6(1-x)^-4 second derivative
    3 24(1-x)^-5 third derivative
    NOTICE the lack of negatives on the 1 and 3 derivative.

    The thing that is confusing the heck out of me as well is that when I look for the first derivative of the function (1-x)^-2 on wolfram alpha it gives me -2(1-x)^-3, but when I look for the maclaurin series, the answer does not show the negative sign.

    Please help
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Dec 4, 2012 #2

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    The book is right. You are forgetting to use the chain rule.
     
  4. Dec 4, 2012 #3

    Mark44

    Staff: Mentor

    And in particular, that d/dx(1 - x) = -1
     
  5. Dec 4, 2012 #4
    I feel pretty silly. I very much appreciate the quick responses.
     
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