BCECE Engineering BCECE Engineering Solved Paper-2003

  • question_answer
    The value of the determinant \[\left| \begin{matrix}    x & a & b+c  \\    x & b & c+a  \\    x & c & a+b  \\ \end{matrix} \right|=0\]if:

    A) \[x=a\]                

    B)                   \[x=b\]                               

    C)                   \[x=c\]                

    D)                   \[x\]has any value

    Correct Answer: D

    Solution :

    Let \[\Delta =\left| \begin{matrix}    x & a & b+c  \\    x & b & c+a  \\    x & c & a+b  \\ \end{matrix} \right|\] Applying \[{{C}_{3}}\to {{C}_{2}}+{{C}_{3}}\] \[=x\left| \begin{matrix}    1 & a & a+b+c  \\    1 & b & a+b+c  \\    1 & c & a+b+c  \\ \end{matrix} \right|\] \[=x(a+b+c)\left| \begin{matrix}    1 & a & 1  \\    1 & b & 1  \\    1 & c & 1  \\ \end{matrix} \right|\] \[=0\][\[\because \]two columns are identical] Note: If a determinant have any two rows or columns are identical, then values of determinant is zero.


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