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 determinant \[\,\left| \,\begin{matrix}    1 & 1 & 1  \\    1 & 2 & 3  \\    1 & 3 & 6  \\ \end{matrix}\, \right|\]is not equal to   [MP PET 1988]

    A) \[\left| \,\begin{matrix}    2 & 1 & 1  \\    2 & 2 & 3  \\    2 & 3 & 6  \\ \end{matrix}\, \right|\]

    B) \[\left| \,\begin{matrix}    2 & 1 & 1  \\    3 & 2 & 3  \\    4 & 3 & 6  \\ \end{matrix}\, \right|\]

    C) \[\left| \begin{matrix}    1 & 2 & 1  \\    1 & 5 & 3  \\    1 & 9 & 6  \\ \end{matrix} \right|\]

    D) \[\left| \,\begin{matrix}    3 & 1 & 1  \\    6 & 2 & 3  \\    10 & 3 & 6  \\ \end{matrix} \right|\,\]

    Correct Answer: A

    Solution :

    \[\left| \,\begin{matrix}    1 & 1 & 1  \\    1 & 2 & 3  \\    1 & 3 & 6  \\ \end{matrix}\, \right|\,=\,\left| \,\begin{matrix}    2 & 1 & 1  \\    3 & 2 & 3  \\    4 & 3 & 6  \\ \end{matrix}\, \right|\]    by \[{{C}_{1}}\to {{C}_{1}}+{{C}_{2}}\] = \[a,b,c\], by \[{{C}_{2}}\to {{C}_{2}}+{{C}_{3}}\] = \[\left| \,\begin{matrix}    3 & 1 & 1  \\    6 & 2 & 3  \\    10 & 3 & 6  \\ \end{matrix}\, \right|\], by \[{{C}_{1}}\to {{C}_{1}}+{{C}_{2}}+{{C}_{3}}\]. But \[\ne \left| \,\begin{matrix}    2 & 1 & 1  \\    2 & 2 & 3  \\    2 & 3 & 6  \\ \end{matrix}\, \right|\].


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