CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2009

  • 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)         \[4\]

    E)  \[6\]

    Correct Answer: A

    Solution :

    Given, \[A=\left[ \begin{matrix}    1 & 2  \\    3 & 5  \\ \end{matrix} \right]\] \[\Rightarrow \]               \[|A|=5-6=-1\] \[\therefore \]  \[|{{A}^{200-}}-5{{A}^{2008}}|=|{{A}^{2008}}||A-5I|\]                 \[={{(-1)}^{2008}}\left| \left[ \begin{matrix}    1 & 2  \\    3 & 5  \\ \end{matrix} \right]-\left[ \begin{matrix}    5 & 0  \\    0 & 5  \\ \end{matrix} \right] \right|\]                 \[=\left| \begin{matrix}    -4 & 2  \\    3 & 0  \\ \end{matrix} \right|\]


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