Manipal Engineering Manipal Engineering Solved Paper-2013

  • question_answer
    For two unimodular complex numbers\[{{z}_{1}}\]and\[{{z}_{2}},\,\,{{\left[ \begin{matrix}    {{{\bar{z}}}_{1}} & {{z}_{2}}  \\    {{{\bar{z}}}_{2}} & {{z}_{1}}  \\ \end{matrix} \right]}^{-1}}{{\left[ \begin{matrix}    {{z}_{1}} & {{z}_{2}}  \\    -{{{\bar{z}}}_{2}} & {{{\bar{z}}}_{1}}  \\ \end{matrix} \right]}^{-1}}\]is equal to

    A) \[\left[ \begin{matrix}    {{z}_{1}} & {{z}_{2}}  \\    {{{\bar{z}}}_{1}} & {{{\bar{z}}}_{2}}  \\ \end{matrix} \right]\]                   

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

    C) \[\left[ \begin{matrix}    1/2 & 0  \\    0 & 1/2  \\ \end{matrix} \right]\]   

    D)         None of these

    Correct Answer: C

    Solution :

    \[{{\left[ \begin{matrix}    {{{\bar{z}}}_{1}} & -{{z}_{2}}  \\    {{{\bar{z}}}_{2}} & {{z}_{1}}  \\ \end{matrix} \right]}^{-1}}{{\left[ \begin{matrix}    {{z}_{1}} & {{z}_{2}}  \\    -{{{\bar{z}}}_{2}} & {{{\bar{z}}}_{1}}  \\ \end{matrix} \right]}^{-1}}\] \[={{\left\{ \left[ \begin{matrix}    {{z}_{1}} & {{z}_{2}}  \\    -{{{\bar{z}}}_{2}} & {{{\bar{z}}}_{1}}  \\ \end{matrix} \right]\left[ \begin{matrix}    {{{\bar{z}}}_{1}} & -{{z}_{2}}  \\    {{{\bar{z}}}_{2}} & {{z}_{1}}  \\ \end{matrix} \right] \right\}}^{-1}}\] \[={{\left[ \begin{matrix}    {{z}_{1}}{{{\bar{z}}}_{1}}+{{z}_{2}}{{{\bar{z}}}_{2}} & 0  \\    0 & {{z}_{2}}{{{\bar{z}}}_{2}}+{{z}_{1}}{{{\bar{z}}}_{1}}  \\ \end{matrix} \right]}^{-1}}\] \[={{\left[ \begin{matrix}    |{{z}_{1}}{{|}^{2}}+|{{z}_{2}}{{|}^{2}} & 0  \\    0 & |{{z}_{1}}{{|}^{2}}+|{{z}_{2}}{{|}^{2}}  \\ \end{matrix} \right]}^{-1}}\] \[={{\left[ \begin{matrix}    2 & 0  \\    0 & 2  \\ \end{matrix} \right]}^{-1}}=\left[ \begin{matrix}    1/2 & 0  \\    0 & 1/2  \\ \end{matrix} \right]\]


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