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 ≡ cos2A – sin2A
    or
    cos 2A ≡ 2cos2A – 1
    or
    cos 2A ≡ 1 – 2sin2A
    tan 2A ≡ (2 tan A) / (1 – tan2A)

Example 1

Trigonometric Identities to Prove - Double Angles (1) | ExamSolutions - youtube Video

Example 2

Trigonometric Identities to Prove - Double Angles (2) | ExamSolutions - youtube Video

Example 3

Trigonometric Identities to Prove - Double Angles (3) | ExamSolutions - youtube Video