Double angle formulae sin 2alpha 2sinalphacos alpha cos 2alpha cos2alpha -sin2alpha cos 2alpha 1 - 2 sin2alpha cos 2alpha. Cos 2th 1 - 2sin 2 th Equation 1 cos 2th 2cos 2 th - 1 Equation 2 Note that the equations above are identities meaning the equations are true for any value of the variable th. The tangent of a double angle is a fraction.
For example cos 60 is equal to cos² 30-sin² 30.
The tangent of a double angle is a fraction. This gives cos2A cos 2A sin A cos2 A 1 cos2 A 2cos2 A 1 This is another. So using this result we can replace the term sin2 A in the double angle formula. The double-angle formulas are proved from the sum formulas by putting v.