The online Double Angle Identity Calculator is used to calculate trigonometric functions of angles that are equal to 2θ in terms of θ.
sin(2θ) = 2 x sinθ x cosθ
tan(2θ) = 2 x tanθ / 1 - tan2θ
cos(2θ) = 1 - 2sin2θ
For example, θ = 15o, sin(2θ) = 0.5, cos(2θ) = 0.866025, tan(2θ) = 0.57735.