If R is a relation in N × N defined by (a, b) R (c, d) if and only if ad = bc, show that R is an equivalence relation. -Maths 9th

1 Answer

Answer :

(i) R is reflexive. For all (a, b) ∈ N × N we have (a, b) R (a, b) because ab = ba ⇒ R is reflexive. (ii) R is symmetric. Suppose (a, b) R (c, d) Then (a, b) R (c, d) ⇒ ad = bc ⇒ cb = da ⇒ (c, d) R (a, b) ⇒ R is symmetric. Commutivity of multiplication in N (iii) R is transitive. Suppose (a, b) R (c, d) and (c, d) R (e, f). Then ad = bc and cf = de ⇒ (ad) (cf) = (bc) (de) ⇒ af = be ⇒ (a, b) R (e, f) ⇒ R is transitive. Since R is reflexive, symmetric and transitive, therefore, R is an equivalence relation on N × N.

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