JEE Main & Advanced Mathematics Functions Question Bank Self Evaluation Test - Relations and Functions-I

  • question_answer
    A relation R is defined in the set Z of integers as follows \[(x,y)\in R\] iff \[{{x}^{2}}+{{y}^{2}}=9.\] Which of the following is false?

    A) \[R=\{(0,3),(0,-3),(3,0),(-3,0)\}\]

    B) Domain of \[R=\{-3,0,3\}\]

    C) Range of \[R=\{-3,0,3\}\]

    D) None of these

    Correct Answer: D

    Solution :

    [d] \[{{x}^{2}}+{{y}^{2}}=9\Rightarrow {{y}^{2}}=9-{{x}^{2}}\]
    \[\Rightarrow y=\pm \sqrt{9-{{x}^{2}}}\]
    \[x=0\Rightarrow y=\pm \sqrt{9-0}=\pm 3\in Z\]
    \[x=\pm 1\Rightarrow y=\pm \sqrt{9-1}=\pm \sqrt{8}\notin Z\]
    \[x=\pm 2\Rightarrow y=\pm \sqrt{9-4}=\pm \sqrt{5}\notin Z\]
    \[x=\pm 3\Rightarrow y=\pm \sqrt{9-9}=0\in Z\]
    \[x=\pm 4\Rightarrow y=\pm \sqrt{9-16}=\pm \sqrt{-7}\notin Z\] And so on,
    \[\therefore R=\{(0,3),(0,-3),(3,0),(-3,0)\}\]
    Domain of \[R=\{x:(x,y)\in R\}=\{0,3,-3\}\]
    Range of \[R=\{y:(x,y)\in R\}=\{3,-3,0\}.\]


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