JCECE Engineering JCECE Engineering Solved Paper-2007

  • question_answer
    If\[\left| \begin{matrix}    a+x & a-x & a-x  \\    a-x & a+x & a-x  \\    a+x & -a-x & a-x  \\ \end{matrix} \right|=0\], then\[x\]is equal to

    A) \[0,\,\,2a\]                         

    B) \[a,\,\,2a\]

    C) \[0,\,\,3a\]                         

    D)  none of these

    Correct Answer: C

    Solution :

    Given  \[\left| \begin{matrix}    a+x & a-x & a-x  \\    a-x & a+x & a-x  \\    a-x & a-x & a+x  \\ \end{matrix} \right|=0\] \[\Rightarrow \]             \[\left| \begin{matrix}    3a-x & a-x & a+x  \\    3a-x & a+x & a-x  \\    3a-x & a-x & a+x  \\ \end{matrix} \right|=0\] \[(C\to {{C}_{1}}+{{C}_{2}}+{{C}_{3}})\] \[\Rightarrow \]          \[(3a-x)\left| \begin{matrix}    1 & a-x & a-x  \\    1 & a+x & a-x  \\    1 & a-x & a-x  \\ \end{matrix} \right|=0\] \[\Rightarrow \]               \[(3a-x)\left| \begin{matrix}    1 & a-x & a-x  \\    0 & 2x & 0  \\    0 & 0 & 2x  \\ \end{matrix} \right|=0\]                                                 \[\left[ \begin{align}   & {{R}_{2}}\to {{R}_{2}}-{{R}_{1}} \\  & {{R}_{3}}\to {{R}_{3}}-{{R}_{1}} \\ \end{align} \right]\] \[\Rightarrow \]               \[(3a-x)(4{{x}^{2}})=0\] \[\Rightarrow \]                                     \[x=3a,\,\,0\]


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