# Integral of sqrt(x^2-a^2)exp(-x)

1. May 19, 2009

New to the forum, thanks for having me.

I've looked in tables and tried Mathmatica but have not came
up with a formula for the integral over x of

sqrt(x^2-a^2)exp(-x)

If anyone could point me in the right direction I'd be appreciative.
Thanks

2. May 20, 2009

### Irrational

$$\int\sqrt{x^2-a^2}e^{-x}dx$$

Integration by parts?

There is a standard formula for integrating $$\int\sqrt{x^2-a^2}dx$$ (that involves logs which might help later with the exponential).

Haven't worked it out myself but that's where i'd start.

3. May 20, 2009

### Cyosis

You won't be able to find a primitive.

4. May 20, 2009

### Irrational

yeah. wolfram didn't like it when i plugged it in.

5. May 23, 2009