JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Types of matrices, Algebra of matrices

  • question_answer
    If \[A=\left[ \begin{matrix}    x & 1  \\    1 & 0  \\ \end{matrix} \right]\]and \[{{A}^{2}}\] is the identity matrix, then x = [EAMCET 1993]

    A) 1

    B) 2

    C) 3

    D) 0

    Correct Answer: D

    Solution :

     \[A=\left[ \begin{matrix}    x & 1  \\    1 & 0  \\ \end{matrix} \right],\therefore {{A}^{2}}=I\Rightarrow \left[ \begin{matrix}    x & 1  \\    1 & 0  \\ \end{matrix} \right]\,\left[ \begin{matrix}    x & 1  \\    1 & 0  \\ \end{matrix} \right]=\left[ \begin{matrix}    1 & 0  \\    0 & 1  \\ \end{matrix} \right]\]   Þ \[\left[ \begin{matrix}    {{x}^{2}}+1 & x  \\    x & 1  \\ \end{matrix} \right]=\left[ \begin{matrix}    1 & 0  \\    0 & 1  \\ \end{matrix} \right]\Rightarrow {{x}^{2}}+1=1\Rightarrow x=0\].


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