Indefinite Integral of e raised to a negative fraction

[MathMan09]

Homework Statement

Find the constant, c, that satisfies the following equation:

Homework Equations

The integral is from -infinity to infinity

1 = c $$\int$$ e ^ -|x|/2 *dx

The Attempt at a Solution

c = 1/4

I have the solution given to me, but I do not understand how to get the steps to the answer.

 

[Dick]

Find the integral of e^(-|x|/2) from 0 to infinity (where you can drop the absolute value). Compare that with the integral of the same function from -infinity to 0.