# Homework Help: Integration Help

1. Jan 19, 2009

### negatifzeo

1. The problem statement, all variables and given/known data
$\int {\frac {1}{\sqrt {{e^{x}}+1}}} dx$

3. The attempt at a solution

I tried integration by parts, using ${\frac {1}{\sqrt {{e^{x}}+1}}}$ as u and dx as dv. This seemed to make the problem more complicated. Using e^x+1 as a u substitution won't work either. Any help getting on the right path would be greatly appreciated!
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jan 19, 2009

### rock.freak667

You could try hyperbolic trig sub. such as ex=sinhu

3. Jan 19, 2009

### negatifzeo

I don't know what hyperbolic trig sub. is yet. We've just gotten to integration by parts.

4. Jan 19, 2009

### rock.freak667

Have you done normal trig substitutions? As ex=tan2u looks like it would work out fine

5. Jan 19, 2009

### negatifzeo

Nope. Maybe it's a problem I'm just supposed to try and not succeed at.

6. Jan 19, 2009

### rock.freak667

Did you learn partial fractions yet? If you did try putting $u^2=e^x+1$ and post back what you tried.

7. Jan 19, 2009

### negatifzeo

I'm not sure of the procedure when using that technique. if u^2=e^x+1, then does the integral become 1/u? Then the answer would just be ln(u)... I dont think thats right

8. Jan 19, 2009

### rock.freak667

u^2=e^x +1
then 2u du =e^x dx and e^x=?
and so dx =?

9. Jan 21, 2009

### negatifzeo

This problem is driving me nuts. There was a typo earlier, it's actually e^x-1.

Expanding on what you said, if u^2=e^x-1
2udu=e^xdx and dx=(2udu/e^x). Moving all of this stuff around is just fine and dandy but I don't know where to put it back in.

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