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Q.Show that the relation R in the set {1,2,3}\{1, 2, 3\} given by R={(1,2),(2,1)}R = \{(1, 2), (2, 1)\} is symmetric but neither reflexive nor transitive.

Jammu Kashmir JkboseJKBOSE Class 12 Annual Regular Examination 2025Subjective· 2mImportance★★★★★
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Check each property directly against the definition of RR: it is symmetric, but fails reflexivity and transitivity.

Let A={1,2,3}A = \{1,2,3\} and R={(1,2),(2,1)}R = \{(1,2),(2,1)\}.

Not reflexive: Reflexivity requires (a,a)∈R(a,a)\in R for every a∈Aa\in A. Here (1,1),(2,2),(3,3)(1,1),(2,2),(3,3) are all absent from RR. So RR is not reflexive.

Symmetric: Symmetry requires that whenever (a,b)∈R(a,b)\in R, we also have (b,a)∈R(b,a)\in R. Here (1,2)∈R(1,2)\in R and indeed (2,1)∈R(2,1)\in R; also (2,1)∈R(2,1)\in R and indeed (1,2)∈R(1,2)\in R. So RR is symmetric.

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