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
    If \[a\ne 6,b,c\]satisfy \[\left| \,\begin{matrix}    a & 2b & 2c  \\    3 & b & c  \\    4 & a & b  \\ \end{matrix}\, \right|=0,\]then \[abc=\] [EAMCET 2000]

    A) \[a+b+c\]

    B) 0

    C) \[{{b}^{3}}\]

    D) \[ab+bc\]

    Correct Answer: C

    Solution :

    \[{{A}^{-1}}={{A}^{2}}\]\[{{A}^{3}}=I\] Þ \[(a-6)({{b}^{2}}-ac)=0\Rightarrow {{b}^{2}}-ac=0\], \[=3\left[ \frac{-1+\sqrt{3}i}{2}-\frac{-1-\sqrt{3}i}{2} \right]=3\sqrt{3}\,i\] \[\therefore \] \[ac={{b}^{2}}\Rightarrow abc={{b}^{3}}.\]


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