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

- anonymous

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

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- anonymous

##### 1 Attachment

- nincompoop

can you try without u-sub?

- Astrophysics

Ye, u = lnx

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## More answers

- anonymous

@nincompoop lol no clue

- Astrophysics

You can pull the -9 out as it's just a constant

- anonymous

Ohh right! I always forget that! >.<

- Astrophysics

\[-9 \int\limits \frac{ \left( lnx \right)^2 }{ x } dx\] u = lnx

- anonymous

then dx = (1/x) du

- Astrophysics

\[du = \frac{ 1 }{ x }dx \implies dx= xdu\]

- anonymous

Isn't du/dx = 1/x ?

- Empty

Yeah you're both right :P

- anonymous

Ohh ahah right! I've lost my mind xD

- Astrophysics

This anonymous user who keeps joining makes me lose connection

- 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

Which anon user? :O

- 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

Well, unless you're just subbing in for du, then the x's should get cancelled out

- Astrophysics

\[-9 \int\limits \frac{ u^2 }{ x }xdu\] right/

- anonymous

Wait what just happened? o.o

- Astrophysics

|dw:1437192143650:dw|

- anonymous

Right, followed till here

- 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

Ohhhh OK didn't notice that! Yep, makes sense!

- Astrophysics

Alright cool :D

- Astrophysics

BTW don't forget the +C

- anonymous

True true true!!! XD Haha was about to forget! Lol thanks so much you math genius! :D

- 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

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

- Astrophysics

Yup!

- Astrophysics

+C

- anonymous

Hahaha oh gee m bad XD yes +C

- anonymous

my*

- Astrophysics

\[\huge \checkmark\]

- anonymous

Niiiiiiice how'd you do that?? :O

- Astrophysics

\checkmark lol

- anonymous

lemme try XD

- anonymous

\checkmark

- anonymous

Heyyyyy it aint working :P LOL

- Astrophysics

No no, I meant for latex, so you can put it in the equation bar

- anonymous

\[\checkmark\]

- anonymous

Yours was bigger -.-

- anonymous

Hahahaha

- 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

the \huge makes it bigger :P

- anonymous

Ohhhhh :P smart ;P

- anonymous

can we also put in \super huge checkmark ?? XP would that work?? XD

- Astrophysics

Haha no, but you can experiment with it, large, tiny xD

- Astrophysics

\[\tiny \text{astrophysics}\]

- anonymous

Hahaha thats awesome!! \[\Large BOO! \]
scare ya? :P

- Astrophysics

|dw:1437193445973:dw| ahhhh

- Astrophysics

lol

- anonymous

Hahaha LOL XD

- anonymous

Arighty better close this question before the mathematicians here get pissed at me xD lol

- Astrophysics

Haha, don't have to worry about them ;)

- anonymous

Hahaha *thumbs up*

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