This is a tough problem to simply give a hint on, but I'll give it a shot.
Instead of looking directly at I would suggest looking at Start here and also google "properties of roots of quadratic equations." I have debated whether or not to mention the specific result from this search which will be relevant and have decided to leave it out for now; that said, the fact needed will be one of the first results.
This is a bit vague, but it sounded like you wanted to get this one for yourself. Let me know if you need a bit more, or if anything is unclear. Good luck!