anonymous
  • anonymous
Would I have to use the 'u' substitution method to solve this integral?
Mathematics
katieb
  • katieb
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anonymous
  • anonymous
nincompoop
  • nincompoop
can you try without u-sub?
Astrophysics
  • Astrophysics
Ye, u = lnx

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anonymous
  • anonymous
@nincompoop lol no clue
Astrophysics
  • Astrophysics
You can pull the -9 out as it's just a constant
anonymous
  • anonymous
Ohh right! I always forget that! >.<
Astrophysics
  • Astrophysics
\[-9 \int\limits \frac{ \left( lnx \right)^2 }{ x } dx\] u = lnx
anonymous
  • anonymous
then dx = (1/x) du
Astrophysics
  • Astrophysics
\[du = \frac{ 1 }{ x }dx \implies dx= xdu\]
anonymous
  • anonymous
Isn't du/dx = 1/x ?
Empty
  • Empty
Yeah you're both right :P
anonymous
  • anonymous
Ohh ahah right! I've lost my mind xD
Astrophysics
  • Astrophysics
This anonymous user who keeps joining makes me lose connection
anonymous
  • anonymous
kk so then.... \[-9\int\limits \frac{u^2}{x}(\frac{1}{x})du = -9\int\limits \frac{ u^2 }{ x^2 }du\] right?
anonymous
  • anonymous
Which anon user? :O
Astrophysics
  • Astrophysics
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
Astrophysics
  • Astrophysics
Well, unless you're just subbing in for du, then the x's should get cancelled out
Astrophysics
  • Astrophysics
\[-9 \int\limits \frac{ u^2 }{ x }xdu\] right/
anonymous
  • anonymous
Wait what just happened? o.o
Astrophysics
  • Astrophysics
|dw:1437192143650:dw|
anonymous
  • anonymous
Right, followed till here
Astrophysics
  • Astrophysics
|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.
anonymous
  • anonymous
Ohhhh OK didn't notice that! Yep, makes sense!
Astrophysics
  • Astrophysics
Alright cool :D
Astrophysics
  • Astrophysics
BTW don't forget the +C
anonymous
  • anonymous
True true true!!! XD Haha was about to forget! Lol thanks so much you math genius! :D
Astrophysics
  • Astrophysics
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
anonymous
  • anonymous
SO final answer would be \[-9(\frac{ (lnx)^3 }{ 3 })\] ... i think :P haha
Astrophysics
  • Astrophysics
Yup!
Astrophysics
  • Astrophysics
+C
anonymous
  • anonymous
Hahaha oh gee m bad XD yes +C
anonymous
  • anonymous
my*
Astrophysics
  • Astrophysics
\[\huge \checkmark\]
anonymous
  • anonymous
Niiiiiiice how'd you do that?? :O
Astrophysics
  • Astrophysics
\checkmark lol
anonymous
  • anonymous
lemme try XD
anonymous
  • anonymous
\checkmark
anonymous
  • anonymous
Heyyyyy it aint working :P LOL
Astrophysics
  • Astrophysics
No no, I meant for latex, so you can put it in the equation bar
anonymous
  • anonymous
\[\checkmark\]
anonymous
  • anonymous
Yours was bigger -.-
anonymous
  • anonymous
Hahahaha
Astrophysics
  • Astrophysics
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
Astrophysics
  • Astrophysics
the \huge makes it bigger :P
anonymous
  • anonymous
Ohhhhh :P smart ;P
anonymous
  • anonymous
can we also put in \super huge checkmark ?? XP would that work?? XD
Astrophysics
  • Astrophysics
Haha no, but you can experiment with it, large, tiny xD
Astrophysics
  • Astrophysics
\[\tiny \text{astrophysics}\]
anonymous
  • anonymous
Hahaha thats awesome!! \[\Large BOO! \] scare ya? :P
Astrophysics
  • Astrophysics
|dw:1437193445973:dw| ahhhh
Astrophysics
  • Astrophysics
lol
anonymous
  • anonymous
Hahaha LOL XD
anonymous
  • anonymous
Arighty better close this question before the mathematicians here get pissed at me xD lol
Astrophysics
  • Astrophysics
Haha, don't have to worry about them ;)
anonymous
  • anonymous
Hahaha *thumbs up*

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