Let $R_{1}$ and $R_{2}$ be two relations defined on $\mathbb{R}$ by
$a \,R_{1} \,b \Leftrightarrow a b \geq 0$ and $a \,R_{2} \,b \Leftrightarrow a \geq b$
Then,
Solution
<p>$a\,{R_1}\,b \Leftrightarrow ab \ge 0$</p>
<p>So, definitely $(a,a) \in {R_1}$ as ${a^2} \ge 0$</p>
<p>If $(a,b) \in {R_1} \Rightarrow (b,a) \in {R_1}$</p>
<p>But if $(a,b) \in {R_1},(b,c) \in {R_1}$</p>
<p>$\Rightarrow$ Then $(a,c)$ may or may not belong to R<sub>1</sub></p>
<p>{Consider $a = - 5,b = 0,c = 5$ so $(a,b)$ and $(b,c) \in {R_1}$ but $ac < 0$}</p>
<p>So, R<sub>1</sub> is not equivalence relation</p>
<p>$a\,{R_2}\,b \Leftrightarrow a \ge b$</p>
<p>$(a,a) \in {R_2} \Rightarrow$ so reflexive relation</p>
<p>If $(a,b) \in {R_2}$ then $(b,a)$ may or may not belong to R<sub>2</sub></p>
<p>$\Rightarrow$ So not symmetric</p>
<p>Hence it is not equivalence relation</p>
About this question
Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations
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