1.

Three relations R1, R2 and R3 are defined on a set A = {a, b, c} as follows: R1 = {(a, a), (a, b), (a, c), (b, b), (b, c), (c, a), (c, b), (c, c)}R2 = {(a, a)}R3 = {(b, c)}R4 = {(a, b), (b, c), (c, a)}.Find whether or not each of the relations R1, R2, R3, R4 on A is(i) reflexive (ii) symmetric and (iii) transitive.

Answer»

(i) Consider as R1

Given that R1 = {(a, a), (a, b), (a, c), (b, b), (b, c), (c, a), (c, b), (c, c)}

Now let us check R1 is reflexive, symmetric and transitive

Reflexive:

Given (a, a), (b, b) and (c, c) ∈ R1

Clearly, R1 is reflexive.

Symmetric:

We see that the ordered pairs obtained by interchanging the components of R1 are also in R1.

So, R1 is symmetric.

Transitive:

Here, (a, b) ∈ R1, (b, c) ∈ R1 and also (a, c) ∈ R1

So, R1 is transitive.

(ii) Consider as R2

Given that R2 = {(a, a)}

Reflexive:

Clearly (a, a) ∈ R2.

So, R2 is reflexive.

Symmetric:

Clearly (a, a) ∈ R ⇒ (a, a) ∈ R.

So, R2 is symmetric.

Transitive:

R2 is clearly a transitive relation, since there is only one element in it.

(iii) Consider as R3

Given that R3 = {(b, c)}

Reflexive:

Here,(b, b) ∉ R3 neither (c, c) ∉ R3

Clearly, R3 is not reflexive.

Symmetric:

Here, (b, c) ∈ R3, but (c, b) ∉ R3

So, R3 is not symmetric.

Transitive:

Here, R3 has only two elements.

Hence, R3 is transitive.

(iv) Consider as R4

Given that R4 = {(a, b), (b, c), (c, a)}.

Reflexive:

Here, (a, a) ∉ R4, (b, b) ∉ R4 (c, c) ∉ R4

Clearly, R4 is not reflexive.

Symmetric:

Here, (a, b) ∈ R4, but (b, a) ∉ R4.

So, R4 is not symmetric

Transitive:

Here, (a, b) ∈ R4, (b, c) ∈ R4, but (a, c) ∉ R4

Clearly, R4 is not transitive.



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