RAJASTHAN ­ PET Rajasthan PET Solved Paper-2010

  • question_answer
    The roots of the equation\[\left| \begin{matrix}    x & \alpha  & 1  \\    \beta  & x & 1  \\    \beta  & \gamma  & 1  \\ \end{matrix} \right|=0\]are independent of  

    A)  \[\alpha \]                

    B)  \[\beta \]

    C)  \[\gamma \]                 

    D)  All of these

    Correct Answer: A

    Solution :

     \[\left| \begin{matrix}    x & \alpha  & 1  \\    \beta  & x & 1  \\    \beta  & \gamma  & 1  \\ \end{matrix} \right|=0\] Applying, \[{{R}_{2}}\to {{R}_{2}}-{{R}_{1}},{{R}_{3}}-{{R}_{1}},\]we get \[\left| \begin{matrix}    x & \alpha  & 1  \\    \beta -x & x-\alpha  & 0  \\    \beta -x & \gamma -a & 0  \\ \end{matrix} \right|=0\] \[\Rightarrow \] \[(\beta -x)(\gamma -\alpha )-(\beta -x)(x-\alpha )=0\] \[\Rightarrow \] \[(\beta -x)(\gamma -\alpha -x+\alpha )=0\] \[\Rightarrow \] \[(\beta -x)(\gamma -x)=0\] \[\Rightarrow \] \[x=\beta ,\gamma \] Hence, roots of the given equations are independent of a.


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