Fuoco e Direttrice di una Parabola 2

Help us caption and translate this video on Amara.org: http://www.amara.org/en/v/B2wV/ Esercizi: http://www.khanacademy.org/exercise/parabola_intuition_2 Traduzione in Italiano del video Focus and Directrix of a Parabola 2 http://www.youtube.com/watch?v=1Jm9rREA-uA http://www.khanacademy.org/video/focus-and-directrix-of-a-parabola-2?playlist=Algebra Help us caption & translate this video! http://amara.org/v/B2wV/