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

  • question_answer
    If \[A=\left[ \begin{matrix}    0 & 1  \\    0 & 0  \\ \end{matrix} \right]\], I is the unit matrix of order 2 and a, b are arbitrary constants, then \[{{(aI+bA)}^{2}}\] is equal to

    A) \[{{a}^{2}}I+abA\]

    B) \[{{a}^{2}}I+2abA\]

    C) \[{{a}^{2}}I+{{b}^{2}}A\]

    D) None of these

    Correct Answer: B

    Solution :

    [b] \[{{(aI+bA)}^{2}}={{a}^{2}}{{I}^{2}}+{{b}^{2}}{{A}^{2}}+2ab\,AI\] \[={{a}^{2}}{{I}^{2}}+{{b}^{2}}{{A}^{2}}+2abA\] But \[{{A}^{2}}=\left[ \begin{matrix}    0 & 0  \\    0 & 0  \\ \end{matrix} \right]\therefore \,{{(aI+bA)}^{2}}={{a}^{2}}I+2abA\].


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