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Homework Help: I think my problem solving is absurd.

  1. Nov 28, 2009 #1
    1. The problem statement, all variables and given/known data

    Evaluate the definite integral:

    2. Relevant equations

    [tex]\int u^n du/dx[/tex] = u^(n+1)/(n+1) (n not equal to -1)

    3. The attempt at a solution

    (-1) muliplied by [tex]\int[/tex] (e^-x +2)^-1 (-e^-x) dx = ?

    and if I follow the equation above, I got denominator zero, for I broke the rules 'n is not equal to zero'
    I think I did as the equation. but now what should I do now?

  2. jcsd
  3. Nov 28, 2009 #2


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    Do you know how to integrate

    \int \frac 1 u \, du
  4. Nov 29, 2009 #3
    Let u = e^(-x) + 2
    the du = ...
  5. Nov 29, 2009 #4
  6. Nov 29, 2009 #5


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    So with [tex] u = e^{-x} + 2 [/tex] and [tex] du = -e^{-x} [/tex], what happens to your integral?
  7. Nov 30, 2009 #6
    Thank you for your help. I did like this:




    Can you check is this the right answer?
  8. Nov 30, 2009 #7


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    Looks good. You are correct that the absolute value signs are not needed in the answer, since [tex] e^{-x} + 2 [/tex] is never negative.
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