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anonymous

  • one year ago

Would I have to use the 'u' substitution method to solve this integral?

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  1. anonymous
    • one year ago
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  2. nincompoop
    • one year ago
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    can you try without u-sub?

  3. Astrophysics
    • one year ago
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    Ye, u = lnx

  4. anonymous
    • one year ago
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    @nincompoop lol no clue

  5. Astrophysics
    • one year ago
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    You can pull the -9 out as it's just a constant

  6. anonymous
    • one year ago
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    Ohh right! I always forget that! >.<

  7. Astrophysics
    • one year ago
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    \[-9 \int\limits \frac{ \left( lnx \right)^2 }{ x } dx\] u = lnx

  8. anonymous
    • one year ago
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    then dx = (1/x) du

  9. Astrophysics
    • one year ago
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    \[du = \frac{ 1 }{ x }dx \implies dx= xdu\]

  10. anonymous
    • one year ago
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    Isn't du/dx = 1/x ?

  11. Empty
    • one year ago
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    Yeah you're both right :P

  12. anonymous
    • one year ago
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    Ohh ahah right! I've lost my mind xD

  13. Astrophysics
    • one year ago
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    This anonymous user who keeps joining makes me lose connection

  14. anonymous
    • one year ago
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    kk so then.... \[-9\int\limits \frac{u^2}{x}(\frac{1}{x})du = -9\int\limits \frac{ u^2 }{ x^2 }du\] right?

  15. anonymous
    • one year ago
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    Which anon user? :O

  16. Astrophysics
    • one year ago
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    Oh it shows up for me then I refresh haha...but when you do a u sub, you should not have any x's in your integrand

  17. Astrophysics
    • one year ago
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    Well, unless you're just subbing in for du, then the x's should get cancelled out

  18. Astrophysics
    • one year ago
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    \[-9 \int\limits \frac{ u^2 }{ x }xdu\] right/

  19. anonymous
    • one year ago
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    Wait what just happened? o.o

  20. Astrophysics
    • one year ago
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    |dw:1437192143650:dw|

  21. anonymous
    • one year ago
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    Right, followed till here

  22. Astrophysics
    • one year ago
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    |dw:1437192220267:dw| sorry I forgot it was squared, so you can just edit that, but this is the method, it should make more sense since I wrote it out as well haha.

  23. anonymous
    • one year ago
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    Ohhhh OK didn't notice that! Yep, makes sense!

  24. Astrophysics
    • one year ago
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    Alright cool :D

  25. Astrophysics
    • one year ago
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    BTW don't forget the +C

  26. anonymous
    • one year ago
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    True true true!!! XD Haha was about to forget! Lol thanks so much you math genius! :D

  27. Astrophysics
    • one year ago
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    http://www.wolframalpha.com/input/?i=integrate+%28-9%28lnx%29%5E2%29%2Fx+dx is what you should get even though you don't need wolfram for this xD

  28. anonymous
    • one year ago
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    SO final answer would be \[-9(\frac{ (lnx)^3 }{ 3 })\] ... i think :P haha

  29. Astrophysics
    • one year ago
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    Yup!

  30. Astrophysics
    • one year ago
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    +C

  31. anonymous
    • one year ago
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    Hahaha oh gee m bad XD yes +C

  32. anonymous
    • one year ago
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    my*

  33. Astrophysics
    • one year ago
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    \[\huge \checkmark\]

  34. anonymous
    • one year ago
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    Niiiiiiice how'd you do that?? :O

  35. Astrophysics
    • one year ago
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    \checkmark lol

  36. anonymous
    • one year ago
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    lemme try XD

  37. anonymous
    • one year ago
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    \checkmark

  38. anonymous
    • one year ago
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    Heyyyyy it aint working :P LOL

  39. Astrophysics
    • one year ago
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    No no, I meant for latex, so you can put it in the equation bar

  40. anonymous
    • one year ago
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    \[\checkmark\]

  41. anonymous
    • one year ago
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    Yours was bigger -.-

  42. anonymous
    • one year ago
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    Hahahaha

  43. Astrophysics
    • one year ago
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    Yay, you can also right click on peoples latex and go on "show math as" and it will show what they used, so I also put \huge checkmark

  44. Astrophysics
    • one year ago
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    the \huge makes it bigger :P

  45. anonymous
    • one year ago
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    Ohhhhh :P smart ;P

  46. anonymous
    • one year ago
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    can we also put in \super huge checkmark ?? XP would that work?? XD

  47. Astrophysics
    • one year ago
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    Haha no, but you can experiment with it, large, tiny xD

  48. Astrophysics
    • one year ago
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    \[\tiny \text{astrophysics}\]

  49. anonymous
    • one year ago
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    Hahaha thats awesome!! \[\Large BOO! \] scare ya? :P

  50. Astrophysics
    • one year ago
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    |dw:1437193445973:dw| ahhhh

  51. Astrophysics
    • one year ago
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    lol

  52. anonymous
    • one year ago
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    Hahaha LOL XD

  53. anonymous
    • one year ago
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    Arighty better close this question before the mathematicians here get pissed at me xD lol

  54. Astrophysics
    • one year ago
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    Haha, don't have to worry about them ;)

  55. anonymous
    • one year ago
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    Hahaha *thumbs up*

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