Definition:Cosine/Real Function

Definition
The real function $\cos: \R \to \R$ is defined as:


 * $\displaystyle \cos x = \sum_{n \mathop = 0}^\infty \left({-1}\right)^n \frac {x^{2n}}{\left({2n}\right)!} = 1 - \frac {x^2} {2!} + \frac {x^4} {4!} - \cdots$

Also see

 * Cosine Function is Absolutely Convergent