RAJASTHAN ­ PET Rajasthan PET Solved Paper-2011

  • question_answer
    If\[\alpha ,\beta \]and\[\gamma \]are the roots of the equation \[{{x}^{3}}+px+q=0,\]then value of the determinant \[\left| \begin{matrix} \alpha  & \beta  & \gamma   \\ \beta  & \gamma  & \alpha   \\ \gamma  & \alpha  & \beta   \\ \end{matrix} \right|\]is

    A)  \[p\]                

    B)  \[q\]

    C)  \[{{p}^{2}}-2q\]         

    D)  \[0\]

    Correct Answer: D

    Solution :

     Since,\[\alpha ,\beta ,\gamma \]are the roots of \[{{x}^{3}}+px+q=0\] \[\therefore \] \[\alpha +\beta +\gamma =0\] \[\therefore \] \[\left| \begin{matrix}    \alpha  & \beta  & \gamma   \\    \beta  & \gamma  & \alpha   \\    \gamma  & \alpha  & \beta   \\ \end{matrix} \right|\] \[{{R}_{1}}\to {{R}_{1}}+{{R}_{2}}+{{R}_{3}},\]we get \[=\left| \begin{matrix}    \alpha +\beta +\gamma  & \alpha +\beta +\gamma  & \alpha +\beta +\gamma   \\    \beta  & \gamma  & \alpha   \\    \gamma  & \alpha  & \beta   \\ \end{matrix} \right|=0\]


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