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Q.Test whether the relation R={(m,n):m+n is not divisible by 3}R=\{(m,n):m+n\text{ is not divisible by }3\} on Z\mathbb{Z} is reflexive or transitive.

Odisha ChseOdisha CHSE +2 Science Board Exam 2026Subjective· 2mImportance★★★★★
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R={(m,n):m+n is not divisible by 3}R=\{(m,n): m+n\text{ is not divisible by }3\} on Z\mathbb Z is neither reflexive nor transitive.

Reflexivity: We need (m,m)∈R(m,m)\in R for every m∈Zm\in\mathbb Z, i.e. 2m2m not divisible by 33 for every mm. But take m=3m=3: 2m=62m=6, which is divisible by 33, so (3,3)∉R(3,3)\notin R.

⇒R\Rightarrow R is not reflexive.

Transitivity: We look for m,n,pm,n,p with (m,n)∈R(m,n)\in R, (n,p)∈R(n,p)\in R, but (m,p)∉R(m,p)\notin R.

Take m=2, n=3, p=1m=2,\ n=3,\ p=1:

  • m+n=2+3=5m+n=2+3=5, not divisible by 33 ⇒(2,3)∈R\Rightarrow (2,3)\in R. …

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