JCECE Engineering JCECE Engineering Solved Paper-2005

  • question_answer
    The matrix \[\left[ \begin{matrix}    5 & 10 & 3  \\    -2 & -4 & 6  \\    -1 & -2 & b  \\ \end{matrix} \right]\] is a singular matrix, if is equal to:

    A) \[-3\]                                    

    B) \[3\]

    C) \[0\]                                     

    D)  for any value of\[b\]

    Correct Answer: D

    Solution :

    Key Idea: If any square matrix is singular, then the value of determinant is zero. Let          \[A=\left[ \begin{matrix}    5 & 10 & 3  \\    2 & -4 & 6  \\    -1 & -2 & b  \\ \end{matrix} \right]\] Since, \[A\] is singular. \[\therefore \]  \[\left| \begin{matrix}    5 & 10 & 3  \\    -2 & -4 & 6  \\    -1 & -2 & b  \\ \end{matrix} \right|=0\] \[\Rightarrow \]\[5(-4b+12)-10(-2b+6)+3(4-4)=0\] \[\Rightarrow \]\[-20b+60+20b-60+0=0\] \[\Rightarrow \]\[0=0\] \[\therefore \]The given matrix is singular for any value of\[b\]. Note: For a non-singular matrix, the value of determinant is non-zero.


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