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
    \[\left| \,\begin{matrix}    a-1 & a & bc  \\    b-1 & b & ca  \\    c-1 & c & ab  \\ \end{matrix}\, \right|=\] [RPET 1988]

    A) 0

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

    C) \[{{a}^{3}}+{{b}^{3}}+{{c}^{3}}-3abc\]

    D) None of these

    Correct Answer: D

    Solution :

    \[\left| \,\begin{matrix}    a-1 & a & bc  \\    b-1 & b & ca  \\    c-1 & c & ab  \\ \end{matrix}\, \right|=\left| \,\begin{matrix}    a & a & bc  \\    b & b & ca  \\    c & c & ab  \\ \end{matrix}\, \right|-\left| \,\begin{matrix}    1 & a & bc  \\    1 & b & ca  \\    1 & c & ab  \\ \end{matrix}\, \right|\] = \[-\left| \,\begin{matrix}    a & {{a}^{2}} & 1  \\    b & {{b}^{2}} & 1  \\    c & {{c}^{2}} & 1  \\ \end{matrix}\, \right|=-\left| \,\begin{matrix}    a & {{a}^{2}} & 1  \\    b-a & {{b}^{2}}-{{a}^{2}} & 0  \\    c-a & {{c}^{2}}-{{a}^{2}} & 0  \\ \end{matrix}\, \right|\] [By\[{{R}_{2}}\to {{R}_{2}}-{{R}_{1}};\,{{R}_{3}}\to {{R}_{3}}-{{R}_{1}}\]] = \[-(a-b)\,(b-c)\,(c-a)\].


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