The double angle identities are trigonometric identities that give the cosine and sine of a double angle in terms of the cosine and sine of a single angle.
Two additional double angle identities are sometimes given that combine the pythagorean identity and the cosine identity above using algebra.
The double identities can be derived a number of ways:
- Using the sum of two angles identities and algebra
- Using the inscribed angle theorem and the unit circle
- Using the the trigonometry of the complex plane
Derive Double Angle Identities (Algebra)Wumbo (internal)
Derive Double Angles Identities (Unit Circle)Wumbo (internal)
Derive Double Angles Identities (Complex Plane)Wumbo (internal)