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dan815 Group Title

integrate x/lnx

  • one year ago
  • one year ago

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  1. Xavier Group Title
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    With ln(x) in the denominator like that that's not one of our preatty integrals.

    • one year ago
  2. satellite73 Group Title
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    you will not find a nice closed form for this one

    • one year ago
  3. dan815 Group Title
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    ah

    • one year ago
  4. dan815 Group Title
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    is it one of those repeating integrating ones

    • one year ago
  5. satellite73 Group Title
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    you mean like if you integrate by parts will you go around in a circle? i don't think so

    • one year ago
  6. satellite73 Group Title
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    i think you will not be able to solve in in the sense that you will not be able to find some nice function \(F\) whose derivative is \(\frac{x}{\ln(x)}\)

    • one year ago
  7. Xavier Group Title
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    It's the type where our general methods of integrating get us nowhere. We have to leave it in the form of an integral and work with it that way.

    • one year ago
  8. dan815 Group Title
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    this is what im trying to evaultate |dw:1363059332628:dw|

    • one year ago
  9. dan815 Group Title
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    is there another method to equate integral like i know this isnt conservative so

    • one year ago
  10. Xavier Group Title
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    That's completly different. If you are integrating with repect to y first then you don't need to worry about the expressions in x -- they are essentially constants.

    • one year ago
  11. inkyvoyd Group Title
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    Wolfram says it's not expressible in terms of elementary functions - http://www.wolframalpha.com/input/?i=integrate+x%2Fln+x

    • one year ago
  12. inkyvoyd Group Title
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    imo you'd best be off solving it numerically

    • one year ago
  13. dan815 Group Title
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    oh hold on i think i got it xD i forgot the lnx cancels if i do dy first

    • one year ago
  14. Xavier Group Title
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    Yup

    • one year ago
  15. dan815 Group Title
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    xavier u got some time to help ?? im working on one of my assigments due in about 6 hours, gonna need help when i get stuck

    • one year ago
  16. Xavier Group Title
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    I'm here on and off. I'll try to help. Sure other people will jump onboard if I take too long

    • one year ago
  17. dan815 Group Title
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    just looking thru the questions so far i think im gonna just have some trouble in the volume integral questions ill tell ya when i get to them

    • one year ago
  18. dan815 Group Title
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    look at this one its about setting the right bounds |dw:1363060518856:dw|

    • one year ago
  19. dan815 Group Title
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    i get why for dx its y^2 to 4 but how much for dy just doing 0 to 2 instead is enough how come it cant be be rootX to 4

    • one year ago
  20. dan815 Group Title
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    but how come*

    • one year ago
  21. Xavier Group Title
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    What is correct there? The diagram or the bounds on your integrals?

    • one year ago
  22. dan815 Group Title
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    the whole thing is correct i just need to covert to an another double integration where im doing it in reverse order dy dx

    • one year ago
  23. dan815 Group Title
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    but before i do that i wanna know why they set up bounds like that

    • one year ago
  24. Xavier Group Title
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    Either the bounds are wrong or the shaded area is incorrect. Having \[y^2 \le x \le 4\] is the larger of the two areas there.

    • one year ago
  25. dan815 Group Title
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    the shaded region is what im integrating over its in the bounds the function is just like a force equation

    • one year ago
  26. dan815 Group Title
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    where z = ysinx^2

    • one year ago
  27. Xavier Group Title
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    Then your bounds on x should be \[0 \le x \le y^2\]

    • one year ago
  28. dan815 Group Title
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    oh nvm i see what u mean the diagram is wrong

    • one year ago
  29. dan815 Group Title
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    so the bottom part shud be the shaded region right

    • one year ago
  30. dan815 Group Title
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    |dw:1363061109806:dw|

    • one year ago
  31. Xavier Group Title
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    Ah ok so you know that the curve your have is y^2=x or y=sqrt(x). So y is bounded above by sqrt(x) and below by 0. And x ranges from 0 to 4

    • one year ago
  32. dan815 Group Title
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    yeah

    • one year ago
  33. dan815 Group Title
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    so if i wanted to switch order of integration to dy dx then

    • one year ago
  34. Xavier Group Title
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    Just use the bounds on y on the inner integral. x bounds go on outer integral \[0 \le y \le \sqrt{x}\ ; 0 \le x \le 4\]

    • one year ago
  35. dan815 Group Title
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    0 to 4 and 0 to root x

    • one year ago
  36. dan815 Group Title
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    ok got it

    • one year ago
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