Manipal Engineering Manipal Engineering Solved Paper-2010

  • question_answer
    For positive numbers\[x,\,\,y,\,\,z\]the numerical value of the determinant \[\left| \begin{matrix}    1 & {{\log }_{x}}y & {{\log }_{x}}z  \\    {{\log }_{y}}x & 1 & {{\log }_{y}}z  \\    {{\log }_{z}}x & {{\log }_{z}}y & 1  \\ \end{matrix} \right|\]

    A)  0                                            

    B)  1

    C)  2                            

    D)         None of these

    Correct Answer: A

    Solution :

    We have,\[\left| \begin{matrix}    1 & {{\log }_{x}}y & {{\log }_{x}}z  \\    {{\log }_{y}}x & 1 & {{\log }_{y}}z  \\    {{\log }_{z}}x & {{\log }_{z}}y & 1  \\ \end{matrix} \right|\]                 \[=\left| \begin{matrix}    1 & \frac{\log y}{\log x} & \frac{\log z}{\log x}  \\    \frac{\log x}{\log y} & 1 & \frac{\log z}{\log y}  \\    \frac{\log x}{\log z} & \frac{\log y}{\log z} & 1  \\ \end{matrix} \right|\] \[=\frac{1}{\log x\cdot \log y\cdot \log z}\left| \begin{matrix}    \log x & \log y & \log z  \\    \log x & \log y & \log z  \\    \log x & \log y & \log z  \\ \end{matrix} \right|=0\]                                          [\[\because \] all rows are identical]


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