CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2007

  • question_answer
    On the set N of all natural numbers define the relation R by aRb if and only if the GCD of a and b is 2, then R is

    A)  reflexive, but not symmetric

    B)  symmetric only

    C)  reflexive and transitive

    D)  reflexive, symmetric and transitive

    E)  not reflexive, not symmetric and not transitive

    Correct Answer: B

    Solution :

    The relation R is defined by\[aRb,\]if and only if the GCD of a and b is 2. (i)\[oRa,\]then GCD of a and a is a. \[\therefore \]R is not reflexive       (ii) \[aRb\Rightarrow bRa\] If GCD of a and b is 2, then GCD of b and a is 2. \[\therefore \] R is symmetric (iii) \[aRb,\text{ }bRc\Rightarrow cRa\] If GCD of a and b is 2 and GCD of b and c is 2, then it is need not to be GCD of c and a is 2. \[\therefore \]R is not transitive.


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