JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Mock Test - Matrices

  • question_answer
    If A and B are two matrices such that \[AB=B\]and \[BA=A,\]then

    A)  \[{{({{A}^{5}}-{{B}^{5}})}^{3}}=A-B\]

    B)  \[{{({{A}^{5}}-{{B}^{5}})}^{3}}={{A}^{3}}-{{B}^{3}}\]

    C)  \[A-B\]is idempotent

    D)  \[A-B\]is nilpotent

    Correct Answer: D

    Solution :

    [d] Since AB=B and BA=A, so \[BAB={{B}^{2}}\] Or \[(BA)B={{B}^{2}}\] Or \[AB={{B}^{2}}\] Or \[B={{B}^{2}}\] Hence, B is idempotent and similarly A. \[{{(A-B)}^{2}}={{A}^{2}}-AB-BA+{{B}^{2}}\] \[=A-B-A+B=0\] Therefore, A-B is nilpotent.


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