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

  • question_answer
    The inverse of matrix \[A=\left[ \begin{matrix}    0 & 1 & 0  \\    1 & 0 & 0  \\    0 & 0 & 1  \\ \end{matrix} \right]\]is  [Karnataka CET 1993]

    A) A

    B) \[{{A}^{T}}\]

    C) \[\left[ \begin{matrix}    1 & 0 & 0  \\    0 & 1 & 0  \\    0 & 0 & 1  \\ \end{matrix} \right]\]

    D) \[\left[ \begin{matrix}    1 & 0 & 0  \\    1 & 0 & 0  \\    0 & 1 & 0  \\ \end{matrix} \right]\]

    Correct Answer: A

    Solution :

    \[A=\left[ \begin{matrix}    0 & 1 & 0  \\    1 & 0 & 0  \\    0 & 0 & 1  \\ \end{matrix} \right]\] \[\Rightarrow \] \[|A|=-1(1+0)=-1\] \[adj(A)=\,\left[ \,\begin{matrix}    {{A}_{11}} & {{A}_{21}} & {{A}_{31}}  \\    {{A}_{12}} & {{A}_{22}} & {{A}_{32}}  \\    {{A}_{13}} & {{A}_{23}} & {{A}_{33}}  \\ \end{matrix}\, \right]\] \[\frac{{{(-1)}^{3+2}}{{M}_{32}}}{-2},\,\text{  }=\frac{-(-2)}{-2}=-1\] \[{{A}_{11}}=0,\,{{A}_{12}}=-1,\,{{A}_{13}}=0\]  \[{{A}_{21}}=-1,\,{{A}_{22}}=0,\,{{A}_{23}}=0\]   \[{{A}_{31}}=0\], \[{{A}_{32}}=0,{{A}_{33}}=-1\] \[\frac{{{(-1)}^{3+2}}{{M}_{32}}}{-2},\,\text{  }=\frac{-(-2)}{-2}=-1\]  \[{{A}^{-1}}=\frac{adj\,(A)}{|A|}=\left[ \,\begin{matrix}    0 & 1 & 0  \\    1 & 0 & 0  \\    0 & 0 & 1  \\ \end{matrix}\, \right]=A\].


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