JEE Main & Advanced JEE Main Paper (Held On 12-Jan-2019 Evening)

  • question_answer
    The set of all values of\[\lambda \]for which the system of linear equations
    \[x-2y-2z=\lambda x\]
    \[x+2y+z=\lambda y\]
    \[-x-y=\lambda z\]
    has a non-trivial solution            
         [JEE Main Online Paper Held On 12-Jan-2019 Evening]

    A) is an empty set                       

    B) contains exactly two elements       

    C) is a singleton

    D) contains more than two elements

    Correct Answer: C

    Solution :

    The given system of linear equations is \[(1-\lambda )x-2y-2z=0\] \[x+(2-\lambda )y+z=0\] \[-x-y\lambda z=0\] Since, it has a non-trivial solution. \[\therefore \]\[\left| \begin{matrix}    1-\lambda  & -2 & -2  \\    1 & 2-\lambda  & 1  \\    -1 & -1 & -\lambda   \\ \end{matrix} \right|=0\] \[\Rightarrow \]\[(1-\lambda )[(2-\lambda )(-\lambda )+1]+2(-\lambda +1)\]\[-2(-1+2-\lambda )=0\] \[\Rightarrow \]\[(1-\lambda )[-2\lambda +{{\lambda }^{2}}+1+2-2]=0\] \[\Rightarrow \]\[(1-\lambda ){{(1-\lambda )}^{2}}=0\Rightarrow {{(1-\lambda )}^{3}}=0\Rightarrow \lambda =1\]


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