• May 3rd 2010, 07:53 PM
helpmeee
is there a formula for integrating fractions??? sorry if this is hard to understand but i need to find the INTEGRAL of x/(2+e^x).
• May 3rd 2010, 08:10 PM
surjective
integrating fractions
Hello,

When facing such problems you should realize that:

$\int \frac{x}{2+e^{x}}dx=\int \left(\frac{1}{2+e^{x}}\cdot x \right)dx$

If you define $f(x)=\frac{1}{2+e^{x}}$ and $g(x)=x$ then you have:

$\int f(x)g(x) dx$

From here you can simply apply the rule of integration by parts.
• May 3rd 2010, 08:22 PM
helpmeee
• May 3rd 2010, 08:27 PM
CalculusCrazed
• May 3rd 2010, 08:34 PM
helpmeee
That made no sense to me.

Please show me with my problem
• May 3rd 2010, 08:49 PM
lovek323
I don't think integration by parts should be used here.

Are you sure this was the question? This integral is rather difficult to evaluate. Cf. Wolfram Alpha
• May 3rd 2010, 08:51 PM
Debsta
Quote:

Originally Posted by lovek323
I don't think integration by parts should be used here.

Are you sure this was the question? This integral is rather difficult to evaluate. Cf. Wolfram Alpha

Yes state the exact question you are having problems with.
• May 3rd 2010, 09:01 PM
CalculusCrazed
Yeah, because I was trying to do this by parts. It is not easy by any means.
• May 3rd 2010, 09:20 PM
There's always an integral involving Li(x) on the AP exam, right you guys? The AP board loves those almost as much as Si(x).
• May 3rd 2010, 09:36 PM
CalculusCrazed
Quote:

There's always an integral involving Li(x) on the AP exam, right you guys? The AP board loves those almost as much as Si(x).

I never took AP and we didn't learn that in calc 1 or 2. What is Li(x) and Si(x)?
• May 4th 2010, 04:10 AM
mr fantastic
Quote:

Originally Posted by helpmeee
is there a formula for integrating fractions??? sorry if this is hard to understand but i need to find the INTEGRAL of x/(2+e^x).

Are there integral terminals, that is, is it a definite integral?
• May 4th 2010, 04:48 AM
skeeter
Quote:

Originally Posted by helpmeee
is there a formula for integrating fractions??? sorry if this is hard to understand but i need to find the INTEGRAL of x/(2+e^x).

no such integration is required on either the AB or BC exam unless it is a definite integral on the calculator part of the exam.