CBSE 2025 · Region 2 · Set 3 · Q27 · 3 marks
Let $\displaystyle \mathrm{R}$ be a relation on set of real numbers R defined as $\displaystyle \{(\mathrm{x}, y): \mathrm{x}-y+\sqrt{3}$ is an irrational number, $\displaystyle \mathrm{x}, y \in \mathbb{\mathrm{R}}\}$ Verify $\displaystyle \mathrm{R}$ for reflexivity, symmetry and transitivity.
Marking-scheme solution
Let $\displaystyle \mathrm{x} \in \mathbb{\mathrm{R}}$. Then we know that $\displaystyle \mathrm{x}-\mathrm{x}+\sqrt{3}=\sqrt{3}$, which is an irrational number.
\[\Rightarrow(\mathrm{x}, \mathrm{x}) \in \mathrm{R}
\]
Hence, R is reflexive.
We have $\displaystyle \sqrt{3}, 2 \in \mathbb{\mathrm{R}}$ such that $\displaystyle \sqrt{3}-2+\sqrt{3}=2(\sqrt{3}-1)$, which is an irrational number
$\displaystyle \Rightarrow(\sqrt{3}, 2) \in \mathrm{R}$.
But, $\displaystyle 2-\sqrt{3}+\sqrt{3}=2$, which is a rational number.
Hence, $\displaystyle \Rightarrow(2, \sqrt{3}) \notin \mathrm{R}$.
-
Therefore, R is not symmetric.
Let $\displaystyle -\sqrt{3}, \sqrt{3}, 2 \in \mathbb{\mathrm{R}}$ such that $\displaystyle (-\sqrt{3}, \sqrt{3}),(\sqrt{3}, 2) \in \mathbb{\mathrm{R}}$.
But, $\displaystyle (-\sqrt{3}, 2) \notin \mathrm{R}$
Therefore, R is not transitive.
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