# Cotangent of Right Angle

## Theorem

$\cot 90^\circ = \cot \dfrac \pi 2 = 0$

where $\cot$ denotes cotangent.

## Proof

 $\displaystyle \cot 90^\circ$ $=$ $\displaystyle \frac {\cos 90^\circ} {\sin 90^\circ}$ Cotangent is Cosine divided by Sine $\displaystyle$ $=$ $\displaystyle \frac 0 1$ Cosine of Right Angle and Sine of Right Angle $\displaystyle$ $=$ $\displaystyle 0$

$\blacksquare$