Mark the correct alternative in the following question:
For real numbers $x$ and $y$, define $x R y$ iff $x-y+\sqrt{2}$ is an irrational number. Then the relation $R$ is
(a) reflexive
(b) symmetric
(c) transitive
(d) none of these
We have,
$R=\{(x, y): x-y+\sqrt{2}$ is an irrational number; $x, y \in \mathbf{R}\}$
As, $x-x+\sqrt{2}=\sqrt{2}$, which is an irrational number
$\Rightarrow(x, x) \in R$
So, $R$ is reflexive relation
Since, $(\sqrt{2}, 2) \in R$
i. e. $\sqrt{2}-2+\sqrt{2}=2 \sqrt{2}-2$, which is an irrational number
but $2-\sqrt{2}+\sqrt{2}=2$, which is a rational number
$\Rightarrow(2, \sqrt{2}) \notin R$
So, $R$ is not symmetric relation
Also, $(\sqrt{2}, 2) \in R$ and $(2,2 \sqrt{2}) \in R$
i. e. $\sqrt{2}-2+\sqrt{2}=2 \sqrt{2}-2$, which is an irrational number and $2-2 \sqrt{2}+\sqrt{2}=2-\sqrt{2}$, which is
also an irrational number
But $\sqrt{2}-2 \sqrt{2}+\sqrt{2}=0$, which is a rational number
$\Rightarrow(\sqrt{2}, 2 \sqrt{2}) \notin R$
So, $R$ is not transitive relation
Hence, the correct alternative is option (a).