JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Special types of matrices, Transpose, Adjoint and Inverse of matrices

  • question_answer
    If \[A=\left( \begin{matrix}    1 & 2 & 0  \\    0 & 1 & 2  \\    2 & 0 & 1  \\ \end{matrix} \right),\]then adj A [RPET 1996]

    A) \[\left( \begin{matrix}    1 & 4 & -2  \\    -2 & 1 & 4  \\    4 & -2 & 1  \\ \end{matrix} \right)\]

    B) \[\left( \begin{matrix}    1 & -2 & 4  \\    4 & 1 & -2  \\    -2 & 4 & 1  \\ \end{matrix} \right)\]

    C) \[\left( \begin{matrix}    1 & 2 & 4  \\    -4 & 1 & 2  \\    -4 & -2 & 1  \\ \end{matrix} \right)\]

    D) None of these

    Correct Answer: B

    Solution :

    \[A=\left[ \begin{matrix}    1 & 2 & 0  \\    0 & 1 & 2  \\    2 & 0 & 1  \\ \end{matrix} \right]\], \[{{A}_{11}}=1,\,{{A}_{21}}=-2,\,{{A}_{31}}=4\] \[{{A}_{12}}=4,\,{{A}_{22}}=1,\,{{A}_{32}}=-2\] \[{{A}_{13}}=-2,\,{{A}_{23}}=4,\,{{A}_{33}}=1\] \[Adj\,(A)=\left[ \begin{matrix}    1 & -2 & 4  \\    4 & 1 & -2  \\    -2 & 4 & 1  \\ \end{matrix} \right]\].


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