CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2003

  • question_answer
    Inverse of the matrix \[\left[ \begin{matrix}    1 & -2  \\    3 & 4  \\ \end{matrix} \right]\] is :

    A)  \[\frac{1}{10}\left[ \begin{matrix}    1 & -2  \\    3 & 4  \\ \end{matrix} \right]\]                   

    B)  \[\frac{1}{10}\left[ \begin{matrix}    4 & 2  \\    -3 & 1  \\ \end{matrix} \right]\]

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

    D)  \[\frac{1}{10}\left[ \begin{matrix}    4 & -2  \\    -3 & 1  \\ \end{matrix} \right]\]

    Correct Answer: B

    Solution :

    We know \[{{A}^{-1}}\frac{ad\,j\,A}{\left| A \right|}\] \[\therefore \]  \[adjA=\left[ \begin{matrix}    4 & 2  \\    -3 & 1  \\ \end{matrix} \right]\]                 \[\left| A \right|=\left| \begin{matrix}    1 & -2  \\    3 & 4  \\ \end{matrix} \right|\]                 \[=4+6=10\] \[\therefore \]  \[{{A}^{-1}}=\frac{ddj\,A}{\left| A \right|}=\frac{1}{10}\left[ \begin{matrix}    4 & 2  \\    -3 & 1  \\ \end{matrix} \right]\]


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