# Integral of an Exponential function

1. Jun 25, 2010

### rabbahs

Hello every one,

I was doing my research and then I simply struck at a point.
The point is that i do not know how to solve the following Integral. I am not at all bad at doing math but some times I got blanked.

so, here is the Integral,

Integral (infinity,u) exponent^(-u) du

result with derivation or with some reference will be highly appreciated.

thanks

2. Jun 25, 2010

### CompuChip

Err, that doesn't really make sense. Do you mean,
$$\int_{u}^\infty e^{-v} \, dv$$
by any chance (with the boundaries in the correct order and where the integration variable is a dummy not occurring in the integration boundary).

3. Jun 25, 2010

### rabbahs

ok, if it is the case then what will be the answer ?

4. Jun 25, 2010

### rabbahs

In a research paper, I found a solution to a similar problem.

5. Jun 25, 2010

### Staff: Mentor

This is not that similar. Your problem, assuming that it is as CompuChip suggested, is
$$\int_u^{\infty} e^{-v}dv$$

First, find an antiderivative using substitution.
Second, evaluate the improper integral using limits.

This is not a very complicated integral.