# hard integration

• March 12th 2009, 02:05 PM
razorfever
hard integration
how do i integrate

(cos x)^2 / (e^x) + 1

i tried integration by parts but that made it even harder and i can't seem to figure out any trig substitution, can this be integrated???
• March 12th 2009, 02:11 PM
iLikeMaths
do u mean $\frac{(\cos x)^2}{e^x +1}$
• March 12th 2009, 02:29 PM
razorfever
yes exactly that
• March 12th 2009, 02:49 PM
iLikeMaths
use integation by parts $\frac {v \frac{du}{dx} - u \frac {dv}{dx}} {v^2}$ where $v =(e^x +1)
,u= \cos^2 x$
• March 12th 2009, 03:30 PM
razorfever
can you be a bit more specific and write out every step
• March 12th 2009, 03:32 PM
iLikeMaths
ok.. i will post it in about 10 mins, cos im still not used to using the LaTex math thing
• March 12th 2009, 03:54 PM
razorfever
this is the same answer as i got ... i thought it was wrong cause it seemed too big

now do you know how i can find the lim as x goes to infinity of this expression
this is involving a series problem in order to find the upper error bound and the remainder
• March 12th 2009, 03:56 PM
iLikeMaths
i differentiated the function instead of integrating
• March 12th 2009, 06:55 PM
Krizalid
Quote:

Originally Posted by razorfever

can this be integrated???

No.