Input given to the function is called domain. In this case input is x and possible values of x has been described below.
\[ -1 \leq \frac{1}{x} \leq 1 \] and X \[\neq \] 0 .....Boundary conditions (domain)
On solving above inequality we can write x \[\leq \] -1 , x \[\geq \] 1 .
On combining these two we can say |x| \[\leq\] 1 which is domain in this case . so any value beyond this limit will give invalid input.
Range is \[\frac{-\pi }{2} , ,\frac{+\pi }{2} \]. where 
is in radian. In degrees output will be [-90 ,90].
