J & K CET Engineering J and K - CET Engineering Solved Paper-2015

  • question_answer
    Let \[G=\{(b,b),\,(b,c),\,(c,c),\,(c,d)\}\]    and \[H=\{(b,a),\,(c,b),\,(d,c)\}\] Then, the number of  elements in the set \[(G\cup H)\oplus {{(G\cup H)}^{-1}}\] where \[\oplus \] denotes the symmetric difference, is

    A)  \[0\]   

    B)  \[2\]    

    C)  \[7\]     

    D)  \[14\]

    Correct Answer: C

    Solution :

    Given, \[G=\{(b,b),\,(b,\,c),\,(c,c),(c,d)\}\] and \[H=\{(b,a),\,(c,b),(d,c)\}\] Now, \[(G\cup H)\,\,\oplus {{(G\cup H)}^{-1}}\] \[=(G\cup H)\oplus (G'\cap H')\] \[[\because \,\,{{(G\cup H)}^{-1}}=G'\cap H']\] \[=\{(G\cup H)-(G'\cap H')\}\cup \{(G'\cap H')-(G\cup H)\}\]\[=\{(G\cup H)\cap (G'\cap H')'\}\] \[\cup \{(G'\cap H')\cap (G\cup H)'\}\] \[[\because \,\,A-B=A\cap B']\] \[=\{(G\cup H)\cap (G\cup H)\}\] \[\cup \{(G'\cap H')\cap (G'\cap H')\}\] \[\Rightarrow \] \[(G\cup H)\cup (G'\cap H')\] \[\Rightarrow \] \[(G\cup H)\cup (G\cup H)'=G\cup H\] \[G\cup H=\{(b,b),(b,c),(c,c),(c,d),(b,a),(c,b),\] \[(d,c)\}\] \[n(G\cup H)=7\]


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