JEE Main & Advanced Mathematics Functions Question Bank Self Evaluation Test - Relation and Functions-II

  • question_answer
    Let \[\rho \] be the relation on the set R of all real numbers defined by setting \[a\rho b\] if f\[\left| a-b \right|\le \frac{1}{2}.\]then, \[\rho \] is

    A) Reflexive and symmetric but not transitive

    B) Symmetric and transitive but not reflexive

    C) Transitive but neither reflexive nor symmetric

    D) None of these

    Correct Answer: A

    Solution :

    [a] \[\rho \] is reflexive, since \[\left| a-a \right|=0<\frac{1}{2}\] for all \[a\in R.\] \[\rho \] is symmetric, since \[\Rightarrow \left| b-a \right|<\frac{1}{2}\] \[\rho \] is not transitive. For. If we take three numbers \[\frac{3}{4},\frac{1}{3},\frac{1}{8}.\] Then, \[\left| \frac{3}{4}-\frac{1}{3} \right|=\frac{5}{12}<\frac{1}{2}\] and \[\left| \frac{1}{3}-\frac{1}{8} \right|=\frac{5}{24}<\frac{1}{2}\] But, \[\left| \frac{3}{4}-\frac{1}{8} \right|=\frac{5}{8}>\frac{1}{2}\] Thus, \[\frac{3}{4}\rho \frac{1}{3}\] and \[\frac{1}{3}\rho \frac{1}{8}\] but \[\frac{3}{4}(\tilde{\ }\rho )\frac{1}{8}\]


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