JCECE Engineering JCECE Engineering Solved Paper-2007

  • question_answer
    The values of \[x\] and \[y\] such that \[y\] satisfy the equation \[(x,\,\,\,y\,\,\,\in \] real numbers)\[{{x}^{2}}-xy+{{y}^{2}}-4x-4y+16=0\]is

    A) \[4,\,\,4\]                                           

    B) \[3,\,\,3\]

    C) \[2,\,\,2\]                                           

    D)  none of these

    Correct Answer: A

    Solution :

    Given,   \[{{x}^{2}}-xy+{{y}^{2}}-4x-4y+16=0\] \[\Rightarrow \]               \[{{x}^{2}}-(y+4)x+{{y}^{2}}-4y+16=0\] For real \[x,\,\,{{(y+4)}^{2}}-4({{y}^{2}}-4y+16)\ge 0\] \[\Rightarrow \]               \[-3{{y}^{2}}+24y-48=0\] \[\Rightarrow \]               \[{{y}^{2}}-8y+16=0\] \[\Rightarrow \]               \[{{(y-4)}^{2}}=0\Rightarrow y=4\] \[\therefore \]  \[x=4\] \[\Rightarrow \]               \[(x,\,\,y)=(4,\,\,4)\]


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