Cotangent of Full Angle

Theorem

 * $\cot 360^\circ = \cot 2 \pi$ is undefined

where $\cot$ denotes cotangent.

Proof
From Cotangent is Cosine divided by Sine:
 * $\cot \theta = \dfrac {\cos \theta} {\sin \theta}$

From Cosine of Full Angle:
 * $\cos 2 \pi = 1$

From Sine of Full Angle:
 * $\sin 2 \pi = 0$

Thus $\cot \theta$ is undefined at this value.