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Let $R\,= \{(x,y) : x,y \in N\, and\, x^2 -4xy +3y^2\, =0\}$, where $N$ is the set of all natural numbers. Then the relation $R$ is
reflexive but neither symmetric nor transitive
symmetric and transitive
reflexive and symmetric,
reflexive and transitive
Solution
$R = \left\{ {\left( {x,y} \right):x,y \in N\,\,and\,\,{x^2} – 4xy + 3{y^2} = 0} \right\}$
Now, ${{x^2} – 4xy + 3{y^2} = 0}$
$ \Rightarrow \left( {x – y} \right)\left( {x – 3y} \right) = 0$
$\therefore x = y$ or $x = 3y$
$\therefore R = \left\{ {\left( {1,1} \right),\left( {3,1} \right),\left( {2,2} \right),\left( {6,2} \right),\left( {3,3} \right),\left( {9,3} \right),…..} \right\}$
Since $\left( {1,1} \right),\left( {2,2,} \right),\left( {3,3} \right)…..$ are preset in the relation, therefore $R$ is reflxive.
Since $(3,1)$ is an element of $R$ but $(1,3)$ is not the element of $R$, therefore $R$ is not symmetric
Here $\left( {3,1} \right) \in R$ and $\left( {1,1} \right) \in R \Rightarrow \left( {3,1} \right) \in R$
$\left( {6,2} \right) \in R$ and $\left( {2,2} \right) \in R \Rightarrow \left( {6,2} \right) \in R$
For all such $\left( {a,b} \right) \in R$ and $\left( {b,c} \right) \in R \Rightarrow \left( {a,b} \right) \in R$
Hence $R$ is transitive.