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

  • question_answer
    If \[A=\left[ \begin{matrix}    1 & 0  \\    2 & 0  \\ \end{matrix} \right],B=\left[ \begin{matrix}    0 & 0  \\    1 & 12  \\ \end{matrix} \right]\], then [DCE 1999]

    A) \[AB=O,BA=O\]

    B) \[AB=O,BA\ne O\]

    C) \[AB\ne O,BA=O\]

    D) \[AB\ne O,BA\ne O\]

    Correct Answer: B

    Solution :

      \[AB=\,\left[ \begin{matrix}    1 & 0  \\    2 & 0  \\ \end{matrix}\, \right]\,\left[ \begin{matrix}    0 & 0  \\    1 & 12  \\ \end{matrix} \right]=\left[ \begin{matrix}    0 & 0  \\    0 & 0  \\ \end{matrix} \right]=O\] while\[BA=\left[ \begin{matrix}    0 & 0  \\    1 & 12  \\ \end{matrix} \right]\,\left[ \begin{matrix}    1 & 0  \\    2 & 0  \\ \end{matrix} \right]=\left[ \begin{matrix}    0 & 0  \\    25 & 0  \\ \end{matrix} \right]\,\ne O\].


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