INtegration by substitution followed by parts:

[O.J.]

... of (x tan^2 x). i don't know how to do it. pls help

 

[cristo]

Well, what have you tried? This is clearly homework! Try writing tanx in terms of sinx and cosx.

 

[O.J.]

i tried that. i even tried using trig identities for the expansion of tan^2 but i got no where. I am lost...

 

[O.J.]

any ideas?

 

[ChaoticLlama]

this is by-parts integration because you have two functions multiplied by each other.
But before you do that you should use a trig identity (think of an identity which will give you an easily integratable trig function).

 

[cristo]

Bruk, please read the PF guidelines here: https://www.physicsforums.com/showthread.php?t=5374, paying particular attention to the part re giving complete solutions to homework/textbook style questions.

 

[Gib Z]

Good work though :P

 

[cristo]

any ideas?

Hint: Do you know an identity for tan²x in terms of, say, sec²x?

Try using this then integrate by parts. Post your work so we can help you.