\int\frac{dx}{1+e^x}

can anyone find the answer. I'm almost fighting the people at physicsforums.com over this problem!

\int\frac{dx}{1+e^x}

can anyone find the answer. I'm almost fighting the people at physicsforums.com over this problem!

Stop fighting, then. They are right, you know. Hint #1: Double check your integral by differentiation. It should return the original function. Hint #2: Use the integrator (http://integrals.wolfram.com/index.jsp). Don't rely on it too much because you won't learn anything that way.

In[1]:=
\!\(∫\(1\/\(1 + \[ExponentialE]\^x\)\) \[DifferentialD]x\)

Out[1]=
\!\(TraditionalForm\`x - log(1 + \[ExponentialE]\^x)\)

This means

\int\frac{1}{1+e^x}dx = x-\log(1-e^x)

I got something different.

I got

\int\frac{1}{1+e^x}dx = x-ln(e^x +1) + C = \ln[{e^x \over e^x +1}] + C

http://i159.photobucket.com/albums/t121/camilus23/etothexproblem.jpg

nevermind, I see I got the same answer as Mathematica, but you just retyped it wrong. You put a minus sign instead of a plus sign.

Yeah sounds like something I'd do.

Yeah sounds like something I'd do.

I got the same problem. I also confuse myself with the "fence post" problem all of the time.

:(

I always have to concentrate hard to get no error, because these things scare me.

I always have to concentrate hard to get no error, because these things scare me.

Well the important thing is to know HOW to do math, not to actually do math ;)

I think you'll find that's maths

Well the important thing is to know HOW to do math, not to actually do math ;)

May be. But details are the evil. I believe without actually doing math, for most of the people it is impossible both to learn how to do math and to express their ideas.

I think you'll find that's maths

This sidetrack has been moved to a new thread in Linguistics:
Maths vs Math. DH, you're the new "originator" of that thread, so you might want to edit the first post a little. Or not - it's OK as it stands.