Tangent of Three Right Angles

Theorem

 * $\tan 270 \degrees = \tan \dfrac {3 \pi} 2$ is undefined

where $\tan$ denotes tangent.

Proof
We have:

But from Tangent of Right Angle, $\tan 90 \degrees$ is undefined.

Hence so is $\tan 270 \degrees$.

Also defined as
Some sources give that:
 * $\tan 270 \degrees = \infty$

but this naïve approach is overly simplistic and cannot be backed up with mathematical rigour.

Also see

 * Sine of Three Right Angles
 * Cosine of Three Right Angles
 * Cotangent of Three Right Angles
 * Secant of Three Right Angles
 * Cosecant of Three Right Angles