You will be expected to be able to prove a trig. identity such as the examples below. In the videos I show you how to set out an identity and what to look for.

This is a tricky topic and one that I find students give in too quickly. Learn your identities and have patience.

Double angle identities

- sin 2A ≡ 2sin A cos A

cos 2A ≡ cos^{2}A – sin^{2}A

or

cos 2A ≡ 2cos^{2}A – 1

or

cos 2A ≡ 1 – 2sin^{2}A

tan 2A ≡ (2 tan A) / (1 – tan^{2}A)