JEE Main & Advanced Sample Paper JEE Main Sample Paper-18

  • question_answer
    If\[\left[ \begin{matrix}    \alpha  & \beta   \\    \gamma  & -\,\alpha   \\ \end{matrix} \right]\]is to be the square root of two-rowed unit matrix, then \[\alpha ,\]\[\beta \] and \[\gamma \] should satisfy the relation

    A)  \[1-{{\alpha }^{2}}+\beta \gamma =0\]

    B)  \[{{\alpha }^{2}}+\beta \gamma -1=0\]

    C)  \[1+{{\alpha }^{2}}+\beta \gamma =0\]               

    D)  \[1-{{\alpha }^{2}}-\beta \gamma =0\]

    Correct Answer: B

    Solution :

     We have\[\left[ \begin{matrix}    \alpha  & \beta   \\    \gamma  & -\alpha   \\ \end{matrix} \right]\,\left[ \begin{matrix}    \alpha  & \beta   \\    \gamma  & -\alpha   \\ \end{matrix} \right]=\left[ \begin{matrix}    1 & 0  \\    0 & 1  \\ \end{matrix} \right]\] \[\Rightarrow \] \[\left[ \begin{matrix}    {{\alpha }^{2}}+\beta \gamma  & 0  \\    0 & {{\alpha }^{2}}+\beta \gamma   \\ \end{matrix} \right]=\left[ \begin{matrix}    1 & 0  \\    0 & 1  \\ \end{matrix} \right]\] \[\Rightarrow \] \[{{\alpha }^{2}}+\beta \gamma -1=0\]


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