JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Self Evaluation Test - Matrices

  • question_answer
    If matrix \[A=\left[ \begin{matrix}    -5 & -8 & 0  \\    3 & 5 & 0  \\    1 & 2 & -1  \\ \end{matrix} \right]\] then find\[tr(A)+tr({{A}^{2}})+tr({{A}^{3}})+...+tr({{A}^{100}})\]

    A) 100

    B) 50

    C) 200

    D) None of these

    Correct Answer: C

    Solution :

    [c] Consider \[{{A}^{2}}=\left[ \begin{matrix}    -5 & -8 & 0  \\    3 & 5 & 0  \\    1 & 2 & -1  \\ \end{matrix} \right]\left[ \begin{matrix}    -5 & -8 & 0  \\    3 & 5 & 0  \\    1 & 2 & -1  \\ \end{matrix} \right]\] \[=\left[ \begin{matrix}    1 & 0 & 0  \\    0 & 1 & 0  \\    0 & 0 & 1  \\ \end{matrix} \right]=I\,\,So\,\,{{A}^{3}}=\left[ \begin{matrix}    -5 & -8 & 0  \\    3 & 5 & 0  \\    1 & 2 & -1  \\ \end{matrix} \right]\] and So on \[tr(A)+tr({{A}^{2}})tr({{A}^{3}})+...+tr({{A}^{100}})\] \[=(-1)+(3)+(-1)+(3)+...+(-1)+(3)=200\]


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