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

  • question_answer
    The adjoint matrix of \[\left[ \begin{matrix}    3 & -3 & 4  \\    2 & -3 & 4  \\    0 & -1 & 1  \\ \end{matrix} \right]\]is [MP PET 2003]

    A) \[\left[ \begin{matrix}    4 & 8 & 3  \\    2 & 1 & 6  \\    0 & 2 & 1  \\ \end{matrix} \right]\]

    B) \[\left[ \begin{matrix}    1 & -1 & 0  \\    -2 & 3 & -4  \\    -2 & 3 & -3  \\ \end{matrix} \right]\]

    C) \[\left[ \begin{matrix}    11 & 9 & 3  \\    1 & 2 & 8  \\    6 & 9 & 1  \\ \end{matrix} \right]\]

    D) \[\left[ \begin{matrix}    1 & -2 & 1  \\    -1 & 3 & 3  \\    -2 & 3 & -3  \\ \end{matrix} \right]\]

    Correct Answer: B

    Solution :

    Let A = \[\left[ \begin{matrix}    3 & -3 & 4  \\    2 & -3 & 4  \\    0 & -1 & 1  \\ \end{matrix} \right]\] Then, \[{{A}_{11}}=1,\,{{A}_{12}}=-2,\,{{A}_{13}}=-2\]    \[{{A}_{21}}=-1\] ,\[{{A}_{22}}=3\],\[{{A}_{23}}=3\]   \[{{A}_{31}}=0\], \[{{A}_{32}}=-4\],\[{{A}_{33}}=-3\] \[adj\,(A)=\left[ \begin{matrix}    {{A}_{11}} & {{A}_{21}} & {{A}_{31}}  \\    {{A}_{12}} & {{A}_{22}} & {{A}_{32}}  \\    {{A}_{13}} & {{A}_{23}} & {{A}_{33}}  \\ \end{matrix} \right]\]\[=\left[ \begin{matrix}    1 & -1 & 0  \\    -2 & 3 & -4  \\    -2 & 3 & -3  \\ \end{matrix} \right]\].


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