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Homework Help: Symmetric arc length of ln(x) and e^x

  1. Mar 21, 2013 #1
    1. The problem statement, all variables and given/known data
    Explain why ∫(1+(1/x2)1/2dx over [1,e] = ∫(1+e2x)1/2dx over [0,1]

    3. The attempt at a solution
    The two original functions are ln(x) and ex and are both symmetrical about the line y = x. If I take either of the functions and translate it over the line y = x the two functions will match up completely. So it seems reasonable that the arc lengths will be the same over some region. If I plug in the bounds 1 and e into ln(x) i get 0, and 1 and if I plug the bounds 0,1 into ex I get 1, and e. I don't really know how it helps but it's something I suppose.
  2. jcsd
  3. Mar 22, 2013 #2


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    Your argument appears sound. Are you looking for a more algebraic justification? It shouldn't be too hard to turn your argument into algebra.
  4. Mar 22, 2013 #3
    I am looking for a more algebraic justification. I'll try and clean it up and post back when I have something, or if I have any questions. Thanks.
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