JEE Main & Advanced Sample Paper JEE Main - Mock Test - 20

  • question_answer
    Let R be the relation on the set R of all real numbers defined by \[a\,R\,b\] if \[\left| a-b \right|\le 1\]. Then R is

    A) Reflexive and symmetric

    B)        Symmetric only

    C)        Transitive only

    D)        Anti-symmetric only

    Correct Answer: A

    Solution :

    \[\left| a-a \right|=0<1\] \[\therefore \,\,\,a\,\,R\,\,a\,\,\forall \,\,a\in R\] \[\therefore \]  R is reflexive. Again \[a\,\,R\,\,b\Rightarrow \,\,\left| a-b \right|\le 1\Rightarrow \left| b-a \right|\le 1\Rightarrow b\,R\,a\] \[\therefore \] R is symmetric. Now, \[1R\frac{1}{2}\] and \[\frac{1}{2}Rl\]but \[\frac{1}{2}\ne 1\] \[\therefore \] R is not anti-symmetric. Further, \[1\,\,R\,\,2\] and \[2\,\,R\,\,3\] but \[1\cancel{R}3,\] \[\left[ \because \,|1-3|=2>1 \right]\] \[\therefore \] R is not transitive.


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