ccdalamp, if you don't understand something about a post, then please respond within the same thread. To post the question over in another thread is rather insulting to Jhevon.
What specifically about Jhevon's answer are you not understanding? Answer that and we can help you out.
By the way, there is a typo in your equation:
is not a parabola, it is an equation for y. To be a parabola one of those y's must be an x. Which is it?