JEE Main & Advanced AIEEE Solved Paper-2005

  • question_answer
    If \[{{A}^{2}}-A+I=O,\] then the inverse of A is       AIEEE  Solved  Paper-2005

    A) \[l-A\]

    B)                        \[A-l\]  

    C)        A                            

    D)        \[A+l\]

    Correct Answer: A

    Solution :

    If A is any square matrix, then \[A\,{{A}^{-1}}=I\] and \[{{A}^{-1}}I={{A}^{-1}}\]. Since,           \[{{A}^{2}}-A+l=O\] \[\Rightarrow \] \[{{A}^{-1}}{{A}^{2}}-{{A}^{-1}}A+{{A}^{-1}}l=O\] (pre-multiply given relation by\[{{A}^{-1}})\] \[\Rightarrow \]\[({{A}^{-1}}A)A-({{A}^{-1}}A)+{{A}^{-1}}=O\] \[\Rightarrow \]\[A-l+{{A}^{-1}}=O\] \[\Rightarrow \]\[{{A}^{-1}}=l-A\]


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