Cosine of Conjugate Angle

Theorem

 * $\map \cos {2 \pi - \theta} = \cos \theta$

where $\cos$ denotes cosine.

That is, the cosine of an angle equals its conjugate.

Also see

 * Sine of Conjugate Angle
 * Tangent of Conjugate Angle
 * Cotangent of Conjugate Angle
 * Secant of Conjugate Angle
 * Cosecant of Conjugate Angle