double Angle formulas are a very practical class of formulas in trigonometric Function. It's the trigonometric Function of the double Angle expressed by the trigonometric Function of the local Angle. In Calculator, it can be used to simplify the Calculator formula and reduce the number of trigonometric Function, and it is also widely used in engineering.

sine alpha sine beta = - 1/2 [cos (alpha + beta) - cos (alpha beta)]

cosαcosβ=1/2[cos(α+β)+cos(α-β)]

sinαcosβ=1/2[sin(α+β)+sin(α-β)]

cosαsinβ=1/2[sin(α+β)-sin(α-β)]