JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Expansion of determinants, Solution of equation in the form of determinants and properties of determinants

  • question_answer
    One of the roots of the given equation \[\left| \,\begin{matrix}    x+a & b & c  \\    b & x+c & a  \\    c & a & x+b  \\ \end{matrix}\, \right|=0\] is  [MP PET 1988, 2002; RPET 1996]

    A) \[-(a+b)\]

    B) \[-(b+c)\]

    C) \[-a\]

    D) \[-(a+b+c)\]

    Correct Answer: D

    Solution :

    \[\left| \,\begin{matrix}    x+a & b & c  \\    b & x+c & a  \\    c & a & x+b  \\ \end{matrix}\, \right|=0\] \[\Rightarrow \] \[(x+a+b+c)\,\left| \,\begin{matrix}    1 & b & c  \\    1 & x+c & a  \\    1 & a & x+b  \\ \end{matrix}\, \right|=0\] , \[=a\{{{a}^{2}}+ab-2{{a}^{2}}-ab]=-{{a}^{3}}=i\] \[\Rightarrow \] \[x=-(a+b+c)\] is one of the root of the equation.


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