Help us caption and translate this video on Amara.org: http://www.amara.org/en/v/B2vb/ Esercizi: http://www.khanacademy.org/exercise/trig_identities_1 Traduzione in Italiano del video Trig identies part 3 (part 5 if you watch the proofs) http://www.youtube.com/watch?feature=player_embedded&v=JXCiFbEMTZ4 http://www.khanacademy.org/video/trig-identies-part-3--part-5-if-you-watch-the-proofs?playlist=Trigonometry