Q.What do you mean by domain of a function ?

A relation from set $A$ to set $B$ is any subset of the Cartesian product $A \times B$ — a chosen collection of ordered pairs connecting some elements of $A$ to some elements of $B$. A function is a relation with one extra condition: every element of $A$ must be paired with exactly one element of $B$, never zero and never more than one. For a function $f: A \to B$, the domain is $A$, the codomain is $B$, and the range is the subset of $B$ actually used as an image — the range can equ …