JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Self Evaluation Test - Determinats

  • question_answer
    If \[f(x)=a+bx+c{{x}^{2}}\]and \[\alpha ,\beta ,\lambda \] are roots of the equation \[{{x}^{3}}=1,\]then \[\left| \begin{matrix}    a & b & c  \\    b & c & a  \\    c & a & b  \\ \end{matrix} \right|\] is equal to

    A) \[f(\alpha )+f(\beta )+f(\lambda )\]

    B) \[f(\alpha )f(\beta )+f(\beta )f(\lambda )+f(\gamma )+f(\alpha )\]

    C) \[f(\alpha )f(\beta )f(\gamma )\]

    D) \[-f(\alpha )f(\beta )f(\gamma )\]

    Correct Answer: D

    Solution :

    [d] \[\left| \begin{matrix}    a & b & c  \\    b & c & a  \\    c & a & b  \\ \end{matrix} \right|=-({{a}^{3}}+{{b}^{3}}+{{c}^{3}}-3abc)\] \[=-(a+b+c)(a+b{{\omega }^{2}}+c\omega )(a+b\omega +c{{\omega }^{2}})\] \[=-f(\alpha )f(\beta )f(\lambda )[\because \,\alpha =1,\,\beta =\omega ,={{\omega }^{2}}]\]


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