JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Self Evaluation Test - Determinats

  • question_answer
    If \[{{A}^{-1}}=\left[ \begin{matrix}    1 & -2  \\    -2 & 2  \\ \end{matrix} \right],\] what is det(A)?

    A) \[2\]

    B) \[-2\]

    C) \[\frac{1}{2}\]

    D) \[-\frac{1}{2}\]

    Correct Answer: D

    Solution :

    [d] We know that det \[(A)=\frac{1}{\det \,({{A}^{-1}})}\] \[{{A}^{-1}}\left[ \begin{matrix}    1 & -2  \\    -2 & 2  \\ \end{matrix} \right]\] \[\Rightarrow \,\left| {{A}^{-1}} \right|=\left| \begin{align}   & \,\,1\,\,\,-2 \\  & -2\,\,\,\,\,2 \\ \end{align} \right|=2-4=-2\] \[\Rightarrow \det (A)=-\frac{1}{2}\]


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