JCECE Engineering JCECE Engineering Solved Paper-2015

  • question_answer
    If \[A\] satisfies the equation\[{{x}^{3}}-5{{x}^{2}}+4x\]\[+\lambda =O\], then \[{{A}^{-1}}\] exists if

    A) \[\lambda \ne 1\]                           

    B) \[\lambda \ne 2\]

    C) \[\lambda \ne -1\]                         

    D) \[\lambda \ne 0\]

    Correct Answer: D

    Solution :

    Since, \[A\] satisfies the equation                 \[{{x}^{3}}-5{{x}^{23}}+4x+\lambda =O\] \[\Rightarrow \]               \[{{A}^{3}}-5{{A}^{2}}+4A+\lambda I=O\] \[\Rightarrow \]               \[A(-{{A}^{2}}+5A-4I)=\lambda I\] \[\Rightarrow \]               \[A\left\{ \frac{1}{\lambda }(-{{A}^{2}}+5A-4I \right\}=I,\]if\[\lambda \ne 0\] Hence,\[{{A}^{-1}}\]exists and is equal to \[\frac{1}{\lambda }-({{A}^{2}}+5A-4I),\]if\[\lambda \ne 0\].


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