When the angles are different. Is One angle Double the Other?
The identities involving the use of the double angle formulae may be useful in cases where one angle is double another so that you can reduce the equation to the same angle then be able to solve it by earlier methods.
- sin 2A ≡ 2sin A cos A
cos 2A ≡ cos2A – sin2A
cos 2A ≡ 2cos2A – 1
cos 2A ≡ 1 – 2sin2A
tan 2A ≡ (2 tan A) / (1 – tan2A)