Answer
Undefined.
Work Step by Step
We can find the tangent of coterminal angle that lies between $0^{\circ}$ and $360^{\circ}$ for convenience.
$\tan450^{\circ}= \tan(450^{\circ}-360^{\circ})=\tan 90^{\circ}$
The terminal side of $90^{\circ}$ angle passes through (0,1). So $x=0,y=1$ and $r=1$.
$\tan 90^{\circ}=\frac{y}{x}=\frac{1}{0}$
As denominator=0, $\tan 450^{\circ}=\tan 90^{\circ}$ is undefined.
