Not defined?

$\begin{aligned} X & = \tan 85^\circ \tan 175^\circ \tan 265^\circ \tan 355^\circ \\ & = \tan 85^\circ \tan 175^\circ \color{#3D99F6} \tan (180^\circ + 85^\circ) \tan (180^\circ + 175^\circ) & \small \color{#3D99F6} \text{Note that }\tan (180^\circ+\theta) = \tan \theta \\ & = \tan^2 85^\circ \tan^2 175^\circ \\ & = \tan^2 85^\circ \tan^2 (180^\circ - 5^\circ) \\ & = \tan^2 85^\circ \tan^2 (- 5^\circ) \\ & = \tan^2 85^\circ (-\tan 5^\circ)^2 \\ & = \tan^2 85^\circ \tan^2 5^\circ \\ & = \tan^2 (90^\circ - 5^\circ)\tan^2 5^\circ & \small \color{#3D99F6} \text{Note that }\tan (90^\circ-\theta) = \cot \theta \\ & = \cot^2 5^\circ \tan^2 5^\circ & \small \color{#3D99F6} \text{Note that }\cot \theta = \frac 1{\tan \theta} \\ & = \frac {\tan^2 5^\circ} {\tan^2 5^\circ} \\ & = \boxed{1} \end{aligned}$