Answer
The calculator displays an error message.
This is because ratio tangent is not defined for angle $90^{\circ}$.
Work Step by Step
In degree mode, the calculator on pressing $90$ first and then $tan$, displays an error message.
Let's try finding value of $\tan 90^{\circ}$ by an alternate method-
$\tan 90^{\circ}$ = $\frac{\sin 90^{\circ}}{\cos 90^{\circ}}$
(ratio identity)
Now from table, substituting the values of $\sin 90^{\circ}$ and $\cos 90^{\circ}$-
$\tan 90^{\circ}$ = $\frac{1}{0}$
Thus $\tan 90^{\circ}$ becomes undefined because division by zero is not defined.
Calculators are also programmed accordingly.
