Trigonometric Functions

Trigonometric Functions of Negative Anglessin(- θ) = -sinθcos(- θ) = cosθtan(- θ) = -tanθSome Useful Relationships Among Trigonometric Functionssin 2 θ + cos2 θ = 1sec 2 θ – tan2 θ = 1csc 2 θ – cot2 θ = 1Double Angle Formulassin2 θ = 2 sin θ cosθcos2 θ = cos 2θ – sin 2 θ = 1-2 sin 2 θ = 2 cos 2 θ -1tanθtan2θ = 21−tan 2 θHalf Angle FormulasNote: in the formulas in this section, the “+” sign is used in the quadrants where the respectivetrigonometric function is positive for angle θ/2, and the “-” sign is used in the quadrants where therespective trigonometric function is negative for angle θ/2.sin θ 2 = ± 1−cosθ2cosθ2 = ± 1cosθ2tan θ 2 = ± 1−cosθ1cosθ = sinθ1cosθ = 1−cosθsinθ