A Double angles identity is written2θ, for example, as sin 2θ, cos 2α, or tan 2x, where 2θ, 2α, and 2x.
The angle measures and the assumption is that you mean sin(2θ), cos(2α), or tan(2x). Because tangent is equal to the ratio of sine and cosine . Therefor its identity comes from their double-angle identities.
Double angle identity
