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
    The value of the determinant \[\left| \,\begin{matrix}    31 & 37 & 92  \\    31 & 58 & 71  \\    31 & 105 & 24  \\ \end{matrix}\, \right|\]is [MP PET 1992]

    A) - 2

    B) 0

    C) 81

    D) None of these

    Correct Answer: B

    Solution :

    \[\left| \,\begin{matrix}    31 & 37 & 92  \\    31 & 58 & 71  \\    31 & 105 & 24  \\ \end{matrix}\, \right|\,=\,\left| \,\begin{matrix}    31 & 37 & 92  \\    0 & 21 & -21  \\    0 & 47 & -47  \\ \end{matrix}\, \right|\];by \[\begin{align}   & {{R}_{3}}\to {{R}_{3}}-{{R}_{2}} \\  & {{R}_{2}}\to {{R}_{2}}-{{R}_{1}} \\ \end{align}\] = \[\left| \,\begin{matrix}    31 & 129 & 92  \\    0 & 0 & -21  \\    0 & 0 & -47  \\ \end{matrix}\, \right|\] = 0;  (by \[{{C}_{2}}\to {{C}_{2}}+{{C}_{3}})\].


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