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How does the int get from that step to this step?

  1. Sep 28, 2007 #1
    Book ex: We were given integral of [tex]\frac{sqrt of x + 4}{x}[/tex]/x dx

    with the substitution u = sqrt{x + 4}
    --> u^2 = x + 4 and x = u^2 - 4
    --> dx = 2u du

    and the int becomes 2*int of [tex]\frac{u^2}{u^2 - 4}[/tex]du

    But how does it go from that to the next step:

    2 int of 1 + [tex]\frac{4}{u^2 - 4}[/tex]du ??????
    Last edited: Sep 28, 2007
  2. jcsd
  3. Sep 28, 2007 #2
    You add and subtract 4 to the numerator and regroup.

    (u^2+4-4)/(u^2 -4) = (u^2-4)/(u^2-4) + 4/(u^2-4) = 1 + 4/(u^2-4)
  4. Sep 28, 2007 #3
    i'm really confused as to what your original problem is


  5. Sep 28, 2007 #4
    is the integral of sqrt (x+4)/x dx -- sorry for the confusion... And how can the book not explain something like that?!!?!?!?!? If i see james stewart on the street I am going to fling pebles at him man.
  6. Sep 28, 2007 #5
    i actually like his textbook, what ch./sect. is this?
  7. Sep 28, 2007 #6
    :rofl: Pebbles?! I guess that'll learn him.
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