Odd Even and Cofunction Trig Identities

I go over some trigonometric identities that you will see in trig, IB math, calculus. They are the six odd even identities and also the cofunction identities. One of the even identities is cos (-x) = cos x, one of the odd identities is sin (-x) = -sin x. One of the cofunction identities is Cosine (90-theta) = sine theta.