What is Reflexive Relation – Definition and Examples

Here you will learn what is reflexive relation on set with definition and examples.

Let’s begin –

What is Reflexive Relation ?

Definition : A relation R on a set A is said to be reflexive if every element of A is related to itself.

Thus, R is reflexive $$\iff$$ (a, a) $$\in$$ R for all a $$\in$$ A.

A relation R on a set A is not reflexive if there exists an element a $$\in$$ A such that (a, a) $$\notin$$ R.

Note : The identity relation on a non-void set A is always a reflexive relation on A. However, a reflexive relation on A is not necessarily the identity relation on A. For example, the relation R = {(a, a), (b, b), (c, c), (a, b) is a reflexive relation on set A = {a, b, c} but it is not the identity relation on A.

Note : The universal relation on a non-void set A is reflexive.

Also Read : Identity Relation with Examples

Given below are some reflexive relation examples.

Example : Let A = {1, 2, 3} be a set. Then R = {(1, 1), (2, 2), (3, 3), (1, 3), (2, 1)} is a reflexive relation on A.

But, $$R_1$$ = {(1, 1), (3, 3), (2, 1), (3, 2)} is not a reflexive relation on A, because 2 $$\in$$ A  but (2, 2) $$\notin$$ $$R_1$$.

Example : Let X be a non-void set and P(X) be the power set of X. A relation R on P(X) defined by (A, B) $$\in$$ R $$\iff$$ A $$\subseteq$$ B is a reflexive relation since every set is subset of itself.

Example  : Let L be the set of all lines in a plane. Then relation R on  L defined by $$(l_1, l_2)$$ $$\in$$ R $$\iff$$ $$l_1$$ is parallel to $$l_2$$ is reflexive, since every line is parallel to itself.