KVPY Sample Paper KVPY Stream-SX Model Paper-23

  • question_answer
    If \[{{\log }_{3x-1}}(x-2)={{\log }_{(9{{x}^{2}}-6x+1)}}(2{{x}^{2}}-10x-2),\] then x equals to

    A) \[9-\sqrt{15}\]

    B) \[3+\sqrt{15}\]

    C) \[2+\sqrt{5}\]

    D) \[6-\sqrt{5}\]

    Correct Answer: B

    Solution :

    We have,\[{{\log }_{(3x-1}})(x-2)=lo{{g}_{(9{{x}^{2}}-6x+1)}}(2{{x}^{2}}-10x-2)\]\[\Rightarrow \]\[{{\log }_{(3x-1)}}(x-2)=lo{{g}_{{{(3x-1)}^{2}}}}(2{{x}^{2}}-10x-2)\]
    \[\Rightarrow \]\[2{{\log }_{(3x-1)}}{{(x-2)}^{2}}=lo{{g}_{(3x-1)}}(2{{x}^{2}}-10x-2)\]\[\Rightarrow \]\[{{(x-2)}^{2}}=2{{x}^{2}}-10x-2\]\[\Rightarrow \]\[{{x}^{2}}-4x+4=2{{x}^{2}}-10x-2\]
    \[\Rightarrow \]\[{{x}^{2}}-6x-6=0\]\[\Rightarrow \]\[x=3\pm \sqrt{15}\]
    \[\therefore \]\[x=3+\sqrt{15},x>2\]


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