Definition:Cosine

Also see

 * Equivalence of Definitions of Cosine of Angle


 * Definition:Sine
 * Definition:Tangent Function
 * Definition:Cotangent
 * Definition:Secant
 * Definition:Cosecant


 * Definition:Hyperbolic Cosine


 * Properties of Real Cosine Function
 * Cosine of Complement equals Sine