Answer
Undefined.
Work Step by Step
We can find the cotangent of coterminal angle that belongs to [$0^{\circ}$,$360^{\circ}$) for convenience.
$\cot(1800^{\circ})= $
$\cot(1800^{\circ}-5\cdot360^{\circ})=\cot 0^{\circ}$
The terminal side of $0^{\circ}$ angle passes through (1,0). So $x=1,y=0$ and $r=1$.
$\cot 0^{\circ}=\frac{x}{y}=\frac{1}{0}$
Denominator=0, $\cot 1800^{\circ}=\cot 0^{\circ}$ is not defined.
