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Mathematics · 2025 · 3 marks
CBSE 2025 · Region 2 · Set 1 · Q27
Let R be a relation defined over N, where N is set of natural numbers, defined as" m R n if and only if m is a multiple of n, m, n ∈ N. "Find whether…
Let R be a relation defined over N, where N is set of natural numbers, defined as"$\displaystyle \mathrm{m} R n$ if and only if $\displaystyle \mathrm{m}$ is a multiple of $\displaystyle n, \mathrm{m}, n \in N$. "Find whether $\displaystyle R$ is reflexive, symmetric and transitive or not.
Marking-scheme solution
Let $\displaystyle x \in N$. Then we know that x is a multiple of itself.
$\displaystyle \Rightarrow x R x$
Hence, R is reflexive.
We have $\displaystyle 2,8 \in N$ such that $\displaystyle 8$ is a multiple of $\displaystyle 2$
$\displaystyle \Rightarrow 8 R 2$
But, $\displaystyle 2$ is not a multiple of $\displaystyle 8$ . Hence, $\displaystyle 2$ is not R -related to 8.
Therefore, R is not symmetric.
Let $\displaystyle x, y, z \in N$ such that $\displaystyle x R y, y R z$
Then $\displaystyle x=\mathrm{m} y, y=n z$ for some $\displaystyle \mathrm{m}, n \in N$
$\displaystyle \Rightarrow x=\mathrm{m} n z \Rightarrow x=p z$, where $\displaystyle p=\mathrm{m} n \in N$. Hence, $\displaystyle x R z$
Therefore, R is transitive.
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CBSE Class 12 Mathematics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.