Secant Function is Even

Theorem
Let $x \in \R$ be a real number.

Let $\sec x$ be the secant of $x$.

Then, whenever $\sec x$ is defined:
 * $\map \sec {-x} = \sec x$

That is, the secant function is even.

Also see

 * Sine Function is Odd
 * Cosine Function is Even
 * Tangent Function is Odd
 * Cotangent Function is Odd
 * Cosecant Function is Odd