Definition:Even Function

Definition
Let $X \subset \R$ be a symmetric set of real numbers:


 * $\forall x \in X: -x \in X$

A real function $f: X \to \R$ is an even function :


 * $\forall x \in X: f \left ({-x}\right) = f \left({x}\right)$

Also see

 * Definition:Odd Function