CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2004

  • question_answer
    If\[X=\left[ \begin{matrix}    1 & 1  \\    1 & 1  \\ \end{matrix} \right],\]then\[{{X}^{n}},\]for \[n\in N,\] is equal to:

    A)  \[{{2}^{n-1}}X\]                              

    B)  \[{{n}^{2}}X\]

    C)  \[nX\]                 

    D)         \[{{2}^{n+1}}X\]

    E)  \[{{2}^{n}}X\]

    Correct Answer: A

    Solution :

    \[\because \]\[X=\left[ \begin{matrix}    1 & 1  \\    1 & 1  \\ \end{matrix} \right]\] \[\therefore \]  \[{{X}^{2}}=\left[ \begin{matrix}    1 & 1  \\    1 & 1  \\ \end{matrix} \right]\left[ \begin{matrix}    1 & 1  \\    1 & 1  \\ \end{matrix} \right]\]                 \[=2\left[ \begin{matrix}    1 & 1  \\    1 & 1  \\ \end{matrix} \right]\] and        \[{{X}^{3}}=\left[ \begin{matrix}    1 & 1  \\    1 & 1  \\ \end{matrix} \right]\left[ \begin{matrix}    2 & 2  \\    2 & 2  \\ \end{matrix} \right]\]                 \[={{2}^{2}}\left[ \begin{matrix}    1 & 1  \\    1 & 1  \\ \end{matrix} \right]\] Similarly, \[{{X}^{n}}={{2}^{n-1}}\left[ \begin{matrix}    1 & 1  \\    1 & 1  \\ \end{matrix} \right]={{2}^{n-1}}X\]


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