Subject:

Reflexive relation on set is a binary element in which every

element is related to itself.

Let A be a set and R be the relation defined in it.

R is set to be reflexive, if (a, a) ∈ R for all a ∈ A that is, every element of A is R-related to itself, in other words aRa for every a ∈ A.

A relation R in a set A is not reflexive if there be at least one element a ∈ A such that (a, a) ∉ R.

Consider, for example, a set A = {p, q, r, s}.

The relation R\(_{1}\) = {(p, p), (p, r), (q, q), (r, r), (r, s), (s, s)} in A is reflexive, since every element in A is R\(_{1}\)-related to itself.

But the relation R\(_{2}\) = {(p, p), (p, r), (q, r), (q, s), (r, s)} is not reflexive in A since q, r, s ∈ A but (q, q) ∉ R\(_{2}\), (r, r) ∉ R\(_{2}\) and (s, s) ∉ R\(_{2}\)

Solved

example of reflexive relation on set:

**1.**

A relation R is defined on the set Z (set of all integers) by “aRb if and only

if 2a + 3b is divisible by 5”, for all a, b ∈ Z.

Examine if R is a reflexive

relation on Z.

**Solution:**

Let a ∈ Z.

## BM7. Binary Relations

Now 2a + 3a = 5a, which is divisible by 5. Therefore

aRa holds for all a in Z i.e. R is reflexive.

**2.**

A relation R is defined on the set Z by “aRb if a – b is divisible by 5” for a,

b ∈ Z.

Examine if R is a reflexive relation on Z.

**Solution:**

Let a ∈ Z. Then a – a is divisible by 5. Therefore aRa holds

for all a in Z i.e.

R is reflexive.

**3.**

Consider the set Z in which a relation R is defined by ‘aRb if and only if a +

3b is divisible by 4, for a, b ∈ Z. Show that R is a reflexive relation on

on setZ.

**Solution:**

Let a ∈ Z. Now a + 3a = 4a, which is divisible by 4.

Therefore

aRa holds for all a in Z i.e. R is reflexive.

**4.**

A relation ρ is defined on the set of all real numbers R by ‘xρy’ if and only

if |x – y| ≤ y, for x, y ∈ R.

Show that the ρ is not reflexive relation.

**Solution:**

The relation ρ is not reflexive as x = -2 ∈ R but |x – x| = 0

which is not less than -2(= x).

● **Set Theory**

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