Let $\mathrm{A}=\{-3,-2,-1,0,1,2,3\}$ and R be a relation on A defined by $x \mathrm{R} y$ if and only if $2 x-y \in\{0,1\}$. Let $l$ be the number of elements in $R$. Let $m$ and $n$ be the minimum number of elements required to be added in R to make it reflexive and symmetric relations, respectively. Then $l+\mathrm{m}+\mathrm{n}$ is equal to:
Solution
<p>$$\begin{aligned}
&\begin{aligned}
& x R y \Leftrightarrow 2 x-y \in\{0,1\} \\
& \Rightarrow \quad y=2 x \text { or } y=2 x-1 \\
& A=\{-3,-2,-1,0,1,2,3\} \\
& \mathrm{R}=\{(-1,-2),(0,0),(1,2),(-1,-3),(0,-1),(1,1), \\
& (2,3)\} \\
& \Rightarrow \quad I=7
\end{aligned}\\
&\text { For } R \text { to be reflexive }(0,0),(1,1) \in R
\end{aligned}$$</p>
<p>But other $(a, a)$ such that $2 a-a \in\{0,1\}$</p>
<p>$\Rightarrow \quad a \in\{0,1\}$</p>
<p>5 other pairs needs to be added $\Rightarrow m=5$</p>
<p>$x R y \Rightarrow y R x$ to be symmetric</p>
<p>$(-1,-2) \Rightarrow(-2,-1)$</p>
<p>$(1,2) \Rightarrow(2,1)$</p>
<p>$(-1,-3) \Rightarrow(-3,-1)$</p>
<p>$(0,-1) \Rightarrow(-1,0)$</p>
<p>$(2,3) \Rightarrow(3,2) \Rightarrow 5$ needs to be added, $n=5$</p>
<p>$\Rightarrow \quad l+m+n=17$</p>
About this question
Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations
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