Khan Academy
Trig Identities Part 3 (Part 5 If You Watch the Proofs), Trigonometry
Sal takes the mystery out of the trigonometric identities by showing how easily they can be derived. He continues with a problem he started in the video �Trig Identities part three (part five if you watch the proofs) and proves the trig...
Khan Academy
Trig Identities Part 2 (Part 4 If You Watch the Proofs)
In this video, Sal reviews the basic trigonometric definitions and identities, including the sum of angle formulas, and then derives the double angle formulas.