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 \[\left| \,\begin{matrix}    3x-8 & 3 & 3  \\    3 & 3x-8 & 3  \\    3 & 3 & 3x-8  \\ \end{matrix}\, \right|=0,\]then the values of x are [RPET 1997]

    A) 0, 2/3

    B) 2/3, 11/3

    C) 1/2, 1

    D) 11/3, 1

    Correct Answer: B

    Solution :

    \[\left| \,\begin{matrix}    3x-8 & 3 & 3  \\    3 & 3x-8 & 3  \\    3 & 3 & 3x-8  \\ \end{matrix}\, \right|=0\] \[{{C}_{1}}\to {{C}_{1}}+{{C}_{2}}+{{C}_{3}}\], we get Þ \[(3x-2)\left| \,\begin{matrix}    1 & 3 & 3  \\    1 & 3x-8 & 3  \\    1 & 3 & 3x-8  \\ \end{matrix}\, \right|=0\] \[{{R}_{1}}\to {{R}_{1}}-{{R}_{2}}\]and \[{{R}_{2}}\to {{R}_{2}}-{{R}_{3}}\], we get Þ \[(3x-2)\left| \,\begin{matrix}    0 & -3x+11 & 0  \\    0 & 3x-11 & -3x+11  \\    1 & 3 & 3x-8  \\ \end{matrix}\, \right|=0\] \[(3x-2)\left[ {{(-3x+11)}^{2}} \right]=0\] \[x=\frac{2}{3}\]or \[x=\frac{11}{3}\,\,\,\,\Rightarrow x=\frac{2}{3},\frac{11}{3}\].


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