double-angle identities | trigonometric double-angle identities

The double-angle formulas are a set of formulas that express trigonometric functions of twice an angle in terms of the trigonometric functions of the original angle.

Formulas expressing trigonometric functions of an angle 2x in terms of functions of an angle x, sin(2x) | = | 2sin x cos x cos(2x) | = | cos^2 x - sin^2 x | = | 2cos^2 x - 1 | = | 1 - 2sin^2 x tan(2x) | = | (2tan x)/(1 - tan^2 x).

half-angle formulas | hyperbolic functions | multiple-angle formulas | prosthaphaeresis formulas | trigonometric addition formulas | trigonometric functions | trigonometry

high school level (California trigonometry standard)