As we know that a relation is a set of ordered pairs.
Also we know that a function is a relation in which no two different ordered pairs have the same first coordinate.
Hence the given ordered pair [tex] (18,2), (12,9) ,(4,2) ,(5,7) [/tex] represents a function.
Here in the ordered pair the x-coordinate represents the domain of the function, while the y-coordinate represents the range of the function.
Hence the domain of the function represented by the above ordered pair is
[tex] D\epsilon \left \{ 18,12,4,5 \right \} [/tex]
