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

  • question_answer
    Consider the matrices \[A=\left[ \begin{matrix}    4 & 6 & -1  \\    3 & 0 & 2  \\    1 & -2 & 5  \\ \end{matrix} \right],B=\left[ \begin{align}   & \begin{matrix}    2 & 4  \\ \end{matrix} \\  & \begin{matrix}    0 & 1  \\ \end{matrix} \\  & \begin{matrix}    -1 & 2  \\ \end{matrix} \\ \end{align} \right],C=\left[ \begin{matrix}    3  \\    1  \\    2  \\ \end{matrix} \right]\] Out of the given matrix products, which one is not defined.

    A) \[{{(AB)}^{T}}C\]

    B) \[{{C}^{T}}C{{(AB)}^{T}}\]

    C) \[{{C}^{T}}AB\]

    D) \[{{A}^{T}}AB{{B}^{T}}C\]

    Correct Answer: B

    Solution :

    [b] \[A\to 3\times 3,B\to 3\times 2,C\to 3\times 1\] \[AB\to 3\times 2\Rightarrow {{(AB)}^{T}}=2\times 3\Rightarrow {{(AB)}^{T}}C\] is defined \[\Rightarrow {{C}^{T}}\to 1\times 3,\Rightarrow {{C}^{T}}C\to 1\times 1\] Hence \[{{C}^{T}}C{{(AB)}^{T}}\] is not defined. Now, \[{{C}^{T}}AB\] is also defined. \[{{A}^{T}}\to 3\times 3,{{B}^{T}}\to 2\times 3;{{A}^{T}}A\to 3\times 3\] \[B{{B}^{T}}\to 3\times 3\Rightarrow {{A}^{T}}AB{{B}^{T}}\to 3\times 3\] \[\Rightarrow {{A}^{T}}AB{{B}^{T}}C\] is defined


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