Integrating e^(-3x) with u-Substitution

[fumoffu]

Homework Statement

before we start, i don't know how to do the integral sign, so we'll use [

I need to integrate
[ e^(-3x) / 1 + e^(-3x)

Homework Equations

I've always had trouble with doing integration with e

The Attempt at a Solution

I used u=1+e^(-3x)
du = -3e^(-3x)

so du/3 = e^(-3x)

I then do

(1/-3) [ u and i end up with the answer 1/-3 (1+e^(-3x)) + c


answer that i am supposed to get is

-1/3ln|1 + e^(-3x)| + C

 

[fumoffu]

nevermind, stupid post. i got it.. :D