JEE Main & Advanced JEE Main Online Paper (Held On 23 April 2013)

  • question_answer
                    Let                 \[\operatorname{R}=\{(x,y):x,y\in \operatorname{N}\] and                 \[{{x}^{2}}-4xy\]                 \[+3{{y}^{2}}=0\},\] where N is the set of all natural  numbers. Then the relation R is :     JEE Main Online Paper ( Held On 23  April 2013 )

    A)                   reflexive but neither symmetric nor transitive

    B)                                          symmetric and transitive.

    C)                                          reflexive and symmetric.

    D)                                          reflexive and transitive.

    Correct Answer: D

    Solution :

                                       \[R=\{(x,y):x,y\in N\,and\,{{x}^{2}}-4xy+3{{y}^{2}}=0\}\] Now,                 \[{{x}^{2}}-4xy+3{{y}^{2}}=0\]                 \[\Rightarrow\]                 \[(x-y)(x-3y)=0\]                 \[\therefore\]                 \[x=y\,or\,x=3y\]                 \[\therefore\]                 \[R=\{(1,1),\}(3,1),(2,2),(6,2),(3,3),(9,3),....\}\] Since (1,1), (2,2), (3,3),...... are present in the relation, therefore R is reflexive. Since (3,1) is an element of R but (1,3) is not the element of R, therefore R is not symmetric Here(3,1)                 \[\in\] R and  (1,1)                 \[\in\]                 \[R\Rightarrow\]  (3,1)                 \[R\Rightarrow\] (6,2)                 \[R\Rightarrow\] and (2,2)                 \[R\Rightarrow\]  (6,2)                 \[R\Rightarrow\] For all such (a, b)                 \[R\Rightarrow\]  and (b, c)                 \[R\Rightarrow\]                 \[\Rightarrow\] (a,c)                 \[\in R\] Hence R is transitive.


You need to login to perform this action.
You will be redirected in 3 sec spinner