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Homework Help: Calc 3 question

  1. Mar 23, 2010 #1
    how can i find a power series representation for a function like f(x)= ln(1+7x)?
     
  2. jcsd
  3. Mar 23, 2010 #2

    Mark44

    Staff: Mentor

    There are at least two ways. One is very mechanical and involves taking the derivatives of your fucntion. The other is probably a lot quicker. Can you find a power series for 7/(1 + 7x) = 1/(x + 1/7)? What's the connection between ln(1 + 7x) and 1/(x + 1/7)?
     
  4. Mar 23, 2010 #3
    Im not really sure what the connection is but i got this at the answer...the sumation from n=1 to infinity -7x^n/n
     
  5. Mar 23, 2010 #4

    Mark44

    Staff: Mentor

    The connection is that d/dx(ln(1 + 7x) = 7/(1 + 7x), or conversely, that ln(1 + 7x) = [itex]\int[/itex]7/(1 + 7x) dx.

    If you didn't understand that connection, how did you get the result that you got? BTW, I'm not sure that your result is right.
     
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