Answer:
the domain after restriction is (-π/2 , + π/2) such that the function f(x)=csc x becomes invertible.
Explanation:
the function f(x) is given by

The domain of
is all the real numbers except nπ where n belongs to integers,and range of
is (-∞ , -1] U [1 , + ∞) and it could be seen from the graph that it repeats this value infinte times.
in order to make the function invertible i.e. 1-1 and onto we restrict our domain in such a way that it takes these values exactly once i.e. there is a unique image of each x-value.
hence, the domain after restriction becomes:(-π/2 , + π/2).