1.

Let I be the set of integers and R be a relation on I defined by R = {(x, y) : (x – y) is divisible by 11, x, y ∈ I}. Then R is(a) An equivalence relation (b) Symmetric only (c) Reflexive only (d) Transitive only

Answer»

(a) An equivalence relation

• For all a ∈I, a – a = 0, which is divisible by 11. 

Thus, (a, a) ∈R for all a ∈N ⇒ R is reflexive 

• Let (a, b) ∈R (a – b) is divisible by 11 

⇒ – (a – b) is divisible by 11 

⇒ (b – a) is divisible by 11 

⇒ (b, a) ∈R 

R is symmetric. 

• Let (x, y) ∈R and (y, z) ∈R 

⇒ (x – y) is divisible by 11 and (y – z) is divisible by 11 

⇒ (x – y) + (y – z) is divisible by 11 

⇒ (x – z) is divisible by 11 

⇒ (x, z) ∈R 

⇒ R is transitive 

∴ R is an equivalence relation.



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