CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2010

  • question_answer
    The points \[(1,0),\] \[(0,1),\] \[(0,0)\]  and \[(2k,3k),k\ne 0\]  are concyclic, if k is

    A) \[\frac{1}{5}\]                                   

    B) \[-\frac{1}{5}\]

    C) \[-\frac{5}{13}\]                                               

    D) \[\frac{5}{13}\]

    Correct Answer: D

    Solution :

    The equation of the circle which passes through the points \[(1,0),\,(0,1)\] and \[(0,0)\] is \[{{x}^{2}}+{{y}^{2}}-x-y=0\]      ….(i) Given  that, the point \[(2k,\,3k)\] is on the circle and form noncyclic circle. Then, it satisfies the Eq. (i)                 \[{{(2k)}^{2}}+{{(3k)}^{2}}-(2k)-(3k)=0\] \[\Rightarrow \]               \[4{{k}^{2}}+9{{k}^{2}}-5k=0\] \[\Rightarrow \]               \[13{{k}^{2}}-5k=0\] \[\Rightarrow \]               \[k(13k-5)=0\] \[\Rightarrow \]               \[k=0\] or \[k=\frac{5}{13}\] Hence,                  \[k=\frac{5}{13}\]


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