1. Feb 29, 2008

### mathguyz

Does anyone here know what the indefinite integal of 1/e^x is?

Im an new member and, this is my first post.

2. Feb 29, 2008

### sutupidmath

i guess u have posted on the wrong forum, but anyways!

$$\int e^{-x} dx= -e^{-x}+c$$

3. Feb 29, 2008

### sutupidmath

here it is how you might want to think about it: i am assuming you know how to integrate this, since it is only a tabelar integral
$$\int e^{x}dx$$, for the other one$$\int e^{-x}dx$$, take the substitution -x=t, so now we have dx=-dt, now substitute back on the integral we get:
$$\int e^{t}(-dt)=-\int e^{t}dt=-e^t+c$$ substituting back for the original variable we get $$-e^{-x}+c$$

4. Feb 29, 2008

### JasonRox

Why not just let u = e^-x?

No need for substitution here.

5. Feb 29, 2008

### sutupidmath

yeah, i know, but since the op was not able to integrate e^-x, i was assuming that approaching this problem like i did, it would make it easier for him/her to understand!