Tangent Function is Odd

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

Let $\tan x$ be the tangent of $x$.

Then, whenever $\tan x$ is defined:
 * $\tan \left({-x}\right) = -\tan x$

That is, the tangent function is odd.

Also see

 * Sine Function is Odd
 * Cosine Function is Even
 * Hyperbolic Tangent Function is Odd