J & K CET Engineering J and K - CET Engineering Solved Paper-2005

  • question_answer
    The determinant \[\left| \begin{matrix}    4+{{x}^{2}} & -6 & -2  \\    -6 & 9+{{x}^{2}} & 3  \\    -2 & 3 & 1+{{x}^{2}}  \\ \end{matrix} \right|\] is not divisible by

    A)  \[x\]             

    B)  \[{{x}^{3}}\]

    C)  \[14+{{x}^{2}}\]      

    D)  \[{{x}^{5}}\]

    Correct Answer: D

    Solution :

    \[\left| \begin{matrix}    4+{{x}^{2}} & -6 & -2  \\    -6 & 9+{{x}^{2}} & 3  \\    -2 & 3 & 1+{{x}^{2}}  \\ \end{matrix} \right|\] \[=(4+{{x}^{2}})[(1+{{x}^{2}})(9+{{x}^{2}})-9]\] \[+6[-6(1+{{x}^{2}})+6]-2[-18+2(9+{{x}^{2}})]\] \[=(4+{{x}^{2}})(9+9{{x}^{2}}+{{x}^{2}}{{x}^{4}}-9)\] \[+6(-6-6{{x}^{2}}+6)-2(-18+18+2{{x}^{2}})\] \[=(4+{{x}^{2}})(10{{x}^{2}}+{{x}^{4}})-36{{x}^{2}}-4{{x}^{2}}\] \[=40{{x}^{2}}+4{{x}^{4}}+10{{x}^{4}}+{{x}^{6}}-40{{x}^{2}}\] \[=14{{x}^{4}}+{{x}^{6}}\] \[={{x}^{4}}({{x}^{2}}+14)\] Which is not divisible by \[{{x}^{5}}\].


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