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

  • question_answer
    If \[A=\left[ \begin{matrix}    i & 0  \\    0 & i/2  \\ \end{matrix} \right]\]\[(i=\sqrt{-1}),\]then \[{{A}^{-1}}\]= [MP PET 1992]

    A) \[\left[ \begin{matrix}    i & 0  \\    0 & i/2  \\ \end{matrix} \right]\]

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

    C) \[\left[ \begin{matrix}    i & 0  \\    0 & 2i  \\ \end{matrix} \right]\]

    D) \[\left[ \begin{matrix}    0 & i  \\    2i & 0  \\ \end{matrix} \right]\]

    Correct Answer: B

    Solution :

    For\[A=\left[ \begin{matrix}    i & 0  \\    0 & i/2  \\ \end{matrix} \right]\], \[adj\,(A)=\left[ \begin{matrix}    i/2 & 0  \\    0 & i  \\ \end{matrix} \right]\] and\[|A|=-\frac{1}{2}\]. \[\therefore \]  \[{{A}^{-1}}=\frac{1}{\Delta }(adj\,A)=\frac{1}{-1/2}\,\left[ \begin{matrix}    i/2 & 0  \\    0 & i  \\ \end{matrix} \right]=\left[ \begin{matrix}    -i & 0  \\    0 & -2i  \\ \end{matrix} \right]\].


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