Let $A=\{1,2,3\}$. The number of relations on $A$, containing $(1,2)$ and $(2,3)$, which are reflexive and transitive but not symmetric, is _________.
Answer (integer)
3
Solution
<p>Transitivity</p>
<p>$(1,2) \in \mathrm{R},(2,3) \in \mathrm{R} \Rightarrow(1,3) \in \mathrm{R}$</p>
<p>For reflexive $(1,1),(2,2)(3,3) \in R$</p>
<p>Now $(2,1),(3,2),(3,1)$</p>
<p>$(3,1)$ cannot be taken</p>
<p>(1) $(2,1)$ taken and $(3,2)$ not taken</p>
<p>(2) $(3,2)$ taken and $(2,1)$ not taken</p>
<p>(3) Both not taken</p>
<p>therefore 3 relations are possible.</p>
About this question
Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations
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