Relation: Let A and B be two sets. Then a relation R from set A to set B is a subset of A x B. Thus, R is a relation to A to B ⇔ R ⊆ A x B.

If R is a relation from a non-void set B and if (a,b) ∈ R, then we write a R b which is read as ‘a is related to b by the relation R’. if (a,b) ∉ R, then we write a R b, and we say that a is not related to b by the relation R.

Domain: Let R be a relation from a set A to a set B. Then the set of all first components or coordinates of the ordered pairs belonging to R is called the domain of R.

Thus, domain of R ={a : (a,b) ∈ R}. The domain of R ⊆ A.

Range: let R be a relation from a set A to a set B. then the set of all second component or coordinates of the ordered pairs belonging to R is called the range of R.

Example 1: R = {(-1, 1), (1, 1), (-2, 4), (2, 4)}.

dom (R) = {-1, 1, -2, 2} and range (R) = {1, 4}

Example 2: R ={(a, b): a, b ∈ N and a + 3b = 12}

dom (R) = {3, 6, 9} and range (R) = {3, 2, 1}