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Integral of e^x/x

  1. Jul 1, 2010 #1
    First of all, I want to clarify that i know the answer is Ei(x). I have found a way to calculate this integral but the result is definetely wrong Anyway, have a look and tell me where is my mistake
    http://docs.google.com/View?id=dd4jpgg_1g8ztn3g5 [Broken]
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jul 1, 2010 #2

    HallsofIvy

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    Many people (and I am one when I am not using my home computer where I know how strong my virus- protection is) will not open "word" files. They are notorious for harboring viruses.
     
  4. Jul 1, 2010 #3
    Really ? Didn't know that... Well, i can garentee it contains only calculus. Apart from that why why would someone upload a doc file with viruses to physics forums?? I hope i learn "latex" soon so i won't need these word documents
     
  5. Jul 1, 2010 #4

    Mark44

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    For at least two reasons: they knew that the file contained a virus and wanted to spread it; they didn't know the file contained a virus. For a person intent on spreading a computer virus, there is nothing sacrosanct about physicsforums.
     
  6. Jul 1, 2010 #5
    How about googledocs???
     
  7. Jul 1, 2010 #6
    It seems that you have missed 1/x in step 2. The final answer you got is just e^x +
    c. How it can be? Can you check step no. 2?

    Regarding MS word one can disable macros and defend from viruses. For me it worked!!
     
  8. Jul 2, 2010 #7
    Here is the google docs equation
    http://docs.google.com/View?id=dd4jpgg_1g8ztn3g5 [Broken]
     
    Last edited by a moderator: May 4, 2017
  9. Jul 2, 2010 #8
    I know it can't be e^x+c ... I didn't miss it!! Check the google document du=1/x dx
     
  10. Jul 2, 2010 #9
    e^lnx = x is true only if x>0 right? I tried conventional method to solve this integral and i got different answer. I have to check my answer.
     
    Last edited: Jul 2, 2010
  11. Jul 2, 2010 #10
    It's the 5th line. [tex]u[/tex] is independent variable here, so [tex]u'=1[/tex].
     
  12. Jul 2, 2010 #11
  13. Jul 2, 2010 #12
    Of course. There can't be a ln(-|x|)
     
  14. Jul 2, 2010 #13
    Really? I thought that since u=g(x) u'=g'(x)=lnx'=1/x
     
  15. Jul 2, 2010 #14
    Gave you WHAT answer? That article doesn't explain where the error is...

    Yes, you are having problems with the chain rule. If v = e^u, then dv/du = e^u, and dv = (e^u)du, which doesn't help solve the integral.
    If you wanted to take dv/dx, then that would equal (dv/du)*(du/dx), but that's not what you're doing... (and won't help any)
     
  16. Jul 3, 2010 #15
    Try this one:
    [tex]e^x\sum_{i=1}^\infty(i-1)!x^{-i}[/tex]
     
  17. Jul 3, 2010 #16
    [tex] e^{elnx} = e^x[/tex] ?
     
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