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Simple ln integration problem

  1. Aug 27, 2007 #1
    I have some stupid trouble with a simple integration. f(x)=ln(x^(1/2))/x

    I try using u substitution. u=ln(x^(1/2)) Then du=1/(x^(1/2)*1/(2x^(1/2))dx=dx/(2x)
    Then dx should be 2xdu Then plugging back in I should have intg(2u*du) which would give me (ln(x^(1/2))^2; yet the answer my calculator gives me is that answer divided by four; it's like the 2 in the u substitution ends up below xdx, but I don't see how that's possible.

    I will greatly appreciate any help.
     
  2. jcsd
  3. Aug 27, 2007 #2

    learningphysics

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    The calculator is giving you [tex]\frac{1}{4}(lnx)^2[/tex] which is the same as your answer. Notice that the calculator gives lnx, not ln(x^(1/2)). It just took the exponent out of the ln.
     
  4. Aug 27, 2007 #3
    Stupid Calculator! Lol, thanks a lot. I knew there must have been something really idiotic at the bottom, but being a bit OCD I couldn't rest until I found the cause, and I wasted more than an hour with this problem :). Well thanks again, now I can sleep.
     
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