If, instead, you meant tan-1x (i.e. the angle whose tangent is x) then choose atan (press 2nd then atan on the calculator here), which is the same thing.
tan raise to -1 = $${\frac{{\mathtt{1}}}{\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{tan}}{\left({\mathtt{x}}\right)}}} = {cot}{\left({\mathtt{x}}\right)}$$
If, instead, you meant tan-1x (i.e. the angle whose tangent is x) then choose atan (press 2nd then atan on the calculator here), which is the same thing.
