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Homework Help: Integral of e

  1. Dec 10, 2008 #1
    1. The problem statement, all variables and given/known data

    before we start, i don't know how to do the integral sign, so we'll use [

    I need to integrate
    [ e^(-3x) / 1 + e^(-3x)

    2. Relevant equations

    I've always had trouble with doing integration with e

    3. The attempt at a solution

    I used u=1+e^(-3x)
    du = -3e^(-3x)

    so du/3 = e^(-3x)

    I then do

    (1/-3) [ u and i end up with the answer 1/-3 (1+e^(-3x)) + c

    answer that i am supposed to get is

    -1/3ln|1 + e^(-3x)| + C
  2. jcsd
  3. Dec 10, 2008 #2
    nevermind, stupid post. i got it.. :D
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