JEE Main & Advanced Mathematics Sets Question Bank Relations

  • question_answer
    Let S be the set of all real numbers. Then the relation R = {(a, b) : 1 + ab > 0} on S is [NDA 2003]

    A) Reflexive and symmetric but not transitive

    B) Reflexive and transitive but not symmetric

    C) Symmetric, transitive but not reflexive

    D) Reflexive, transitive and symmetric

    E) None of the above is true

    Correct Answer: A

    Solution :

    Since\[1+a.a=1+{{a}^{2}}>0\,,\forall a\in S\], \ \[(a,\,a)\in R\] \ R is reflexive. Also\[(a,b)\in R\] Þ \[1+ab>0\] Þ \[1+ba>0\] Þ\[(b,\,a)\in R\], \ R is symmetric. \[\because (a,\,b)\in R\] and\[(b,\,c)\in R\] need not imply \[(a,\,c)\in R\]. Hence, R is not transitive.


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