CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2007

  • question_answer
    If \[A=\left[ \begin{matrix}    0 & x & 16  \\    x & 5 & 7  \\    0 & 9 & x  \\ \end{matrix} \right]\] is singular, then the possible values of x are

    A)  \[0,12,-12\]    

    B)  \[0,1,-1\]

    C)  \[0,4,-4\]      

    D)  \[0,5,-5\]

    Correct Answer: A

    Solution :

    We have,   \[A=\left[ \begin{matrix}    0 & x & 16  \\    x & 5 & 7  \\    0 & 9 & x  \\ \end{matrix} \right]\] Since, A is singular \[\therefore \]  \[|A|=0\] \[\Rightarrow \]               \[0-x[{{x}^{2}}-0]+16[9x-0]=0\] \[\Rightarrow \]                               \[-{{x}^{3}}+144x=0\] \[\Rightarrow \]                               \[x({{x}^{2}}-144)=0\] \[\Rightarrow \]                               \[x=0,\] \[x=\pm 12\]


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