1.

Let Z be the set of integers. Then the relation R = {(a, b) : a, b ∈ Z and (a + b) is even} defined on Z is(a) Only symmetric (b) Symmetric and transitive only (c) An equivalence relation (d) None of the above

Answer»

(c) An equivalence relation

R is reflexive as (a, a) ∈ R. a + a = 2a is even. 

R is symmetric as (a, b) ∈ R ⇒ (b, a) ∈ R as a + b = b + a = even (Commutative law) 

R is transitive as (a, b) ∈ R and (b, c) ∈ R 

⇒ (a + b) is even and (b + c) is even 

⇒ (a + b) + (b + c) is even 

⇒ (a + 2b + c) is even 

⇒ (a + c) is even as (2b is even) 

⇒ (a, c) ∈ R 

∴ R is an equivalence relation on the set of integers.



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