BCECE Engineering BCECE Engineering Solved Paper-2006

  • question_answer
    The values of a for which the system of equation\[x+y+z=0,\]\[x+ay+az=0,\]\[x-ay+z=0,\] possess non-zero solutions, are given by:

    A)  1, 2                       

    B)        \[1,-1\]                               

    C)  1, 0                       

    D)         none of these

    Correct Answer: B

    Solution :

    The given system of equations possess non-zero solutions.          \[\therefore \]  \[\left| \begin{matrix}    1 & 1 & 1  \\    1 & a & a  \\    1 & -a & 1  \\ \end{matrix} \right|=0\] Applying \[{{R}_{2}}\to {{R}_{2}}-{{R}_{1}}\]and \[{{R}_{3}}\to {{R}_{3}}-{{R}_{1}}\] \[\Rightarrow \]\[\left| \begin{matrix}    1 & 1 & 1  \\    0 & a-1 & a-1  \\    0 & -a-1 & 0  \\ \end{matrix} \right|=0\] \[\Rightarrow \]               \[1\,[0-({{a}^{2}}-)]=0\] \[\Rightarrow \]               \[{{a}^{2}}=1\] \[\Rightarrow \]               \[a=\pm 1.\]


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