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.