# Math Help - Improper Integral problem

1. ## Improper Integral problem

I can't figure out how exactly to do this. If somebody could show me how to set the limits up, that would be great:

Problem:

I need to integrate that, but I've never seen one where both parts of the limits of integration are infinities. Normally I'd use the limit as b approaches infinity from a to b of the integral, but which one is b? I don't get how to start it or set it up.

Thank you for any help.

2. You can just think of it like:

$\lim_{k \to \infty} \int_{-k}^k \frac{dz}{z^2+9}$