CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2009

  • question_answer
    The value of \[\left| \begin{matrix}    1 & {{\log }_{x}}y & {{\log }_{x}}z  \\    {{\log }_{y}}x & 1 & {{\log }_{y}}z  \\    {{\log }_{z}}x & {{\log }_{e}}y & 1  \\ \end{matrix} \right|\] is equal to

    A)  \[0\]                    

    B)  \[1\]

    C)  \[xyz\]              

    D)  \[\log \,xyz\]

    Correct Answer: A

    Solution :

    \[\left| \begin{matrix}    1 & {{\log }_{x}}y & {{\log }_{x}}z  \\    {{\log }_{y}}x & 1 & {{\log }_{y}}z  \\    {{\log }_{e}}x & {{\log }_{e}}x & 1  \\ \end{matrix} \right|\] \[=1(1-{{\log }_{y}}z{{\log }_{z}}y)\] \[-{{\log }_{x}}y({{\log }_{y}}x-{{\log }_{z}}\,x{{\log }_{y}}z)\] \[+{{\log }_{x}}z({{\log }_{z}}y({{\log }_{y}}x-{{\log }_{z}}x)\]                 \[=(1-{{\log }_{y}}y)-{{\log }_{x}}y({{\log }_{y}}x-{{\log }_{y}}x)\]                 \[+{{\log }_{x}}z({{\log }_{z}}x-{{\log }_{z}}x)\]                 \[=(1-1)-0+0=0\]


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