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2 Integration questions.

  1. May 2, 2007 #1
    I need help on these two integration questions:

    1.

    (x^2 -16)/(2x + 8) dx


    2.

    1/(1+9x^2) dx


    I can't seem to find a "u" for either. And I tried a tan identity on number 2 to no avail.
     
  2. jcsd
  3. May 2, 2007 #2

    Office_Shredder

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    Did you try factoring the first one?
     
  4. May 2, 2007 #3
    OH WAIT.....

    Yea so x^2 - 16 would be (x + 4)(x - 4).

    Then I can pull a 1/2 outside, and I'll be left with (x + 4) on the bottom. That will cancel out, so it will be the integral of (x - 4)???
     
  5. May 2, 2007 #4

    HallsofIvy

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    Well, because of that 1/2 you "pulled outside", it will be (1/2) the integral of x-4.

    As far as the second is concerned, you might try letting u= 3x and then think about the derivative of arctan u.
     
  6. May 2, 2007 #5
    Yea thats what I meant.

    Well I tried using 1/(1^2 + (3x)^2).....but that didnt work.
     
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