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

  • question_answer
    If \[A=dig(2,-1,\,3),B=dig(-1,\,3,\,2)\], then \[{{A}^{2}}B=\]

    A) dig (5, 4, 11)

    B) dig (-4, 3, 18)

    C) dig (3, 1, 8 )

    D) B

    Correct Answer: B

    Solution :

    \[{{A}^{2}}B=(A.\,A)B=\left[ \begin{matrix}    2 & 0 & 0  \\    0 & -1 & 0  \\    0 & 0 & 3  \\ \end{matrix} \right]\,\left[ \begin{matrix}    2 & 0 & 0  \\    0 & -1 & 0  \\    0 & 0 & 3  \\ \end{matrix} \right].\,\left[ \begin{matrix}    -1 & 0 & 0  \\    0 & 3 & 0  \\    0 & 0 & 2  \\ \end{matrix} \right]\] \[=\left[ \begin{matrix}    4 & 0 & 0  \\    0 & 1 & 0  \\    0 & 0 & 9  \\ \end{matrix} \right]\,\left[ \begin{matrix}    -1 & 0 & 0  \\    0 & 3 & 0  \\    0 & 0 & 2  \\ \end{matrix} \right]=\left[ \begin{matrix}    -4 & 0 & 0  \\    0 & 3 & 0  \\    0 & 0 & 18  \\ \end{matrix} \right]\].


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