Let a relation $\mathrm{R}$ on $\mathrm{N} \times \mathbb{N}$ be defined as: $\left(x_1, y_1\right) \mathrm{R}\left(x_2, y_2\right)$ if and only if $x_1 \leq x_2$ or $y_1 \leq y_2$. Consider the two statements:
(I) $\mathrm{R}$ is reflexive but not symmetric.
(II) $\mathrm{R}$ is transitive
Then which one of the following is true?
Solution
<p>$$\begin{aligned}
& \left(x_1, y_1\right) R\left(x_2, y_2\right) \\
& \text { If } x_1 \leq x_2 \text { or } y_1 \leq y_2
\end{aligned}$$</p>
<p>For reflexive;</p>
<p>$$\begin{aligned}
& \left(x_1, y_1\right) R\left(x_1, y_1\right) \\
& \Rightarrow x_1 \leq x_1 \text { or } y_1 \leq y_1
\end{aligned}$$</p>
<p>So, $R$ is reflexive</p>
<p>For symmetric</p>
<p>When $\left(x_1, y_1\right) R\left(x_2, y_2\right)$</p>
<p>$\Rightarrow x_1 \leq x_2 \text { or } y_1 \leq y_2$</p>
<p>For $\left(x_2, y_2\right) R\left(x_1, y_1\right)$</p>
<p>$\Rightarrow x_2 \leq x_1 \text { or } y_2 \leq y_1$</p>
<p>Not true for $(1,2)$ and $(3,4)$</p>
<p>For transitive</p>
<p>Take pairs as $(3,9),(4,6),(2,7)$</p>
<p>$(3,9) R(4,6)$</p>
<p>as $4 \geq 3$</p>
<p>$(4,6) R(2,7)$</p>
<p>As $7 \geq 6$</p>
<p>But $(3,9) R(2,7)$</p>
<p>As neither $2 \geq 3$ nor $7 \geq 9$</p>
<p>So not transitive</p>
About this question
Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations
This question is part of PrepWiser's free JEE Main question bank. 195 more solved questions on Sets, Relations and Functions are available — start with the harder ones if your accuracy is >70%.