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

  • question_answer
    If x, y, z are complex numbers, and\[\Delta =\left| \begin{matrix}    0 & -y & -z  \\    {\bar{y}} & 0 & -x  \\    {\bar{z}} & {\bar{x}} & 0  \\ \end{matrix} \right|\] then \[\Delta \] is

    A) Purely real

    B) Purely imaginary

    C) Complex

    D) 0

    Correct Answer: B

    Solution :

    [b] We have \[\overline{\Delta }=\left| \begin{matrix}    0 & -\overline{y} & -\overline{z}  \\    y & 0 & -\overline{x}  \\    z & x & 0  \\ \end{matrix} \right|=\left| \begin{matrix}    0 & y & z  \\    -\overline{y} & 0 & x  \\    -\overline{z} & -\overline{x} & 0  \\ \end{matrix} \right|\] [Interchanging rows and columns] \[={{(-1)}^{3}}\left| \begin{matrix}    0 & -y & -z  \\    \overline{y} & 0 & -x  \\    \overline{z} & \overline{x} & 0  \\ \end{matrix} \right|\] [Taking -1 common from each row] \[=-\Delta \] \[\therefore \overline{\Delta }+\Delta =0\Rightarrow 2\operatorname{Re}(\Delta )=0\] \[\therefore \Delta \] is purely imaginary.


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