# Improper intergrals

1. Oct 14, 2009

### KingSloth

1. The problem statement, all variables and given/known data

$$\int_{-\infty}^{0}e^{-|x|}dx$$
2. Relevant equations

$$\int_{-\infty}^{0}e^{-|x|}dx$$
= $$\int_{-\infty}^{0}e^{-x}dx$$

according to the solution these first two steps is where i go wrong. According to solution, the integral is e^x, which I dont understand. I get e^-x and when I carry out the problem I get -1. The correct answer is 1. Please explain the simplification. thank you
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Oct 14, 2009

### Staff: Mentor

|x| is defined to be equal to x, if x >= 0, and to -x, if x < 0. Your interval over which your are integrating is the negative half of the real line.