Let $\mathrm{A}=\{-4,-3,-2,0,1,3,4\}$ and $\mathrm{R}=\left\{(a, b) \in \mathrm{A} \times \mathrm{A}: b=|a|\right.$ or $\left.b^{2}=a+1\right\}$ be a relation on $\mathrm{A}$. Then the minimum number of elements, that must be added to the relation $\mathrm{R}$ so that it becomes reflexive and symmetric, is __________
Answer (integer)
7
Solution
$$
\begin{aligned}
A & =\{-4,-3,-2,0,1,3,4\} \\\\
R= & \{(-4,4),(-3,3),(0,0),(1,1) \\
& (3,3),(4,4),(0,1),(3,-2)\}
\end{aligned}
$$
<br/><br/>Relation to be reflexive $(a, a) \in R \forall a \in A$
<br/><br/>$\Rightarrow (-4,-4),(-3,-3),(-2,-2)$ also should be added in $R$.
<br/><br/>Relation to be symmetric if $(a, b) \in R$, then $(b, a) \in R \forall a, b \in A$
<br/><br/>$\Rightarrow (4,-4),(3,-3),(1,0),(-2,3)$ also should be added in $R$
<br/><br/>$\Rightarrow$ Minimum number of elements to be added to $R=3+4=7$
About this question
Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations
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