Know and use identities for sin2θ\sin{2θ}sin2θ, cos2θ\cos{2θ}cos2θ, tan2θ\tan{2θ}tan2θ.Includes understanding derivations from sin(θ±ϕ)\sin{(θ \pm ϕ)}sin(θ±ϕ), cos(θ±ϕ)\cos{(θ \pm ϕ)}cos(θ±ϕ), tan(θ±ϕ)\tan{(θ \pm ϕ)}tan(θ±ϕ).cos2θ≡cos2θ−sin2θ\cos{2θ} ≡ \cos^2{θ} - \sin^2{θ}cos2θ≡cos2θ−sin2θcos2θ≡2cos2θ−1\cos{2θ} ≡ 2\cos^2{θ} - 1cos2θ≡2cos2θ−1cos2θ≡1−2sin2θ\cos{2θ} ≡ 1 - 2\sin^2{θ}cos2θ≡1−2sin2θ
