Integrate this (1 Viewer)

[Giant Lobster]

/
| x*arctanx dx
/

I saw my friend do it but i didnt like his method. it required double integrals n stuff. Anyone?

 

[BlackJack]

Use the product rule. (S is the integration symbol)

use:
u= tan^-1 x
du = 1/ (1+x²) dx

v= x² /2
dv = x dx

.'. S x*tan^-1x dx
= x²/2 * tan^-1x - S x²/2 * 1/ (1+x²) dx

= x²/2 * tan^-1x - 1/2 *( S x² / (1+x²) dx )

= x²/2 * tan^-1x - 1/2 *( S 1 - 1/(1+x²) dx )

And it goes from there, rearrange to get:
(1+x²)*tan^-1x / 2 - x/2 + C

 

[Giant Lobster]

damn... this wasnt the question. sorry, i think i remembered wrong.

it was similar to that tho...

edit:

maybe it was S xtanx dx cos i cant seem to do that right now

 

[+Po1ntDeXt3r+]

r u sure bout integrating xtanx?
cos i tried.. nothin..
integrator
S x.tanx dx =
<img src=http://integrals.wolfram.com/graphics.cgi?format=StandardForm&FontSize=Medium&x=43&expr=x%2ATan%5Bx%5D&y=20></IMG>

 

[BlackJack]

Hmmm... someone had asked xtanx before. That would never be asked.

 

[Giant Lobster]

Originally posted by +Po1ntDeXt3r+
r u sure bout integrating xtanx?
cos i tried.. nothin..
integrator
S x.tanx dx =
<img src=http://integrals.wolfram.com/graphics.cgi?format=StandardForm&FontSize=Medium&x=43&expr=x%2ATan%5Bx%5D&y=20></IMG>

Wot the hell is a polylog?! omg...

BJ, r u sure we'll never be asked that? i mean...
heh well i as a power looks a bit too hectic for 4u yeh...

 

[+Po1ntDeXt3r+]

Originally posted by Giant Lobster
Wot the hell is a polylog?! omg...

BJ, r u sure we'll never be asked that? i mean...
heh well i as a power looks a bit too hectic for 4u yeh...

i think so too.. ... u got easier integration to do?

 

[KeypadSDM]

Originally posted by +Po1ntDeXt3r+
i think so too.. ... u got easier integration to do?

Mine don't involve polylog's, so technically they're easier

http://www.boredofstudies.org/community/showthread.php?s=&threadid=24216

 

[Giant Lobster]

damn u guys wats a polylog!!

 

[fitz33]

i couldnt be bothered to try and figure out the notation for polylog on this, so just go here
http://mathworld.wolfram.com/Polylogarithm.html

 

[KeypadSDM]

Jesus. To think i'm 1/4 through my life. There is so much more to learn.

 

[+Po1ntDeXt3r+]

Originally posted by KeypadSDM
Mine don't involve polylog's, so technically they're easier

http://www.boredofstudies.org/community/showthread.php?s=&threadid=24216

I did them already.. they were easy

Originally posted by fitz33
i couldnt be bothered to try and figure out the notation for polylog on this, so just go here
http://mathworld.wolfram.com/Polylogarithm.html

ooooOOOOOooooooOOOOOoooo
preeetttiii lines
man now i want to do uni maths..