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

  • question_answer
    If \[A\left[ \begin{matrix}    1 & 2  \\    3 & 5  \\ \end{matrix} \right],\] then the value of the determinant \[|{{A}^{2009}}-5{{A}^{2008}}|\] is

    A) \[-6\]

    B) \[-5\]

    C) \[-4\]

    D) \[4\]

    Correct Answer: A

    Solution :

    [a] Given, \[A=\left[ \begin{matrix}    1 & 2  \\    3 & 5  \\ \end{matrix} \right]\] \[\Rightarrow \left| A \right|=5-6=-1\] \[\therefore \left| {{A}^{2009}}-5{{A}^{2008}} \right|=\left| {{A}^{2008}} \right|\left| A-5I \right|\] \[={{(-1)}^{2008}}\left| \left[ \begin{matrix}    1 & 2  \\    3 & 5  \\ \end{matrix} \right]-\left[ \begin{matrix}    5 & 0  \\    0 & 5  \\ \end{matrix} \right] \right|=\left| \begin{matrix}    -4 & 2  \\    3 & 0  \\ \end{matrix} \right|=-6\]


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