RAJASTHAN ­ PET Rajasthan PET Solved Paper-2001

  • question_answer
    One root of the equation \[\left| \begin{matrix}    3-x & -6 & 3  \\    -6 & 3-x & 3  \\    3 & 3 & -6-x  \\ \end{matrix} \right|=0\]is

    A)  6               

    B)  3

    C)  0               

    D)  None of these

    Correct Answer: C

    Solution :

     \[\left| \begin{matrix}    3-x & -6 & 3  \\    -6 & 3-x & 3  \\    3 & 3 & -6-x  \\ \end{matrix} \right|=0\] \[\Rightarrow \] \[\left| \begin{matrix}    -x & -x & -x  \\    -6 & 3-x & 3  \\    3 & 3 & -6-x  \\ \end{matrix} \right|\] \[[{{R}_{1}}\to {{R}_{2}}+{{R}_{3}}+{{R}_{1}}]\] \[\Rightarrow \] \[x\left| \begin{matrix}    -1 & -1 & -1  \\    -6 & 3-x & 3  \\    3 & 3 & {}  \\ \end{matrix} \right|=0\] \[\Rightarrow \] \[x=0\]or \[\left| \begin{matrix}    -1 & -1 & -1  \\    -3 & 3-x & 3  \\    3 & 3 & -6-x  \\ \end{matrix} \right|=0\]


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