Definition:Even Function

Definition
Let $X \subset \R$ be a symmetric set, i.e., $x \in X \iff -x \in X$.

A real function $f: X \to \R$ is said to be even if and only if:


 * $f \left ({-x}\right) = f \left({x}\right)$

holds for all $x\in X$.

Also see

 * Odd Function