Help us caption and translate this video on Amara.org: http://www.amara.org/en/v/B2wR/ Traduzione in Italiano del video Proof: Hyperbola Foci http://www.youtube.com/watch?v=HPRFmu7JsKU http://www.khanacademy.org/video/proof--hyperbola-foci?playlist=Algebra Help us caption & translate this video! http://amara.org/v/B2wR/