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

  • question_answer
    \[A=\left| \begin{matrix}    2a & 3r & x  \\    4b & 6s & 2y  \\    -2c & -3t & -z  \\ \end{matrix} \right|=\lambda \left| \begin{matrix}    a & r & x  \\    b & s & y  \\    c & t & z  \\ \end{matrix} \right|,\] then what is the value of \[\lambda \]?

    A) \[12\]

    B) \[-12\]

    C) \[7\]

    D) \[-7\]

    Correct Answer: B

    Solution :

    [b] Given, \[\left| \begin{matrix}    2a & 3r & x  \\    4b & 6s & 2y  \\    -2c & -3t & -z  \\ \end{matrix} \right|=\lambda \left| \begin{matrix}    a & r & x  \\    b & s & y  \\    c & t & z  \\ \end{matrix} \right|\] Taking 2 common from \[{{C}_{1}}\] and 3 from \[{{C}_{2}}\] in LHS \[\therefore \,\,\,2\times 3\left| \begin{matrix}    a & r & x  \\    2b & 2s & 2y  \\    -c & -t & -z  \\ \end{matrix} \right|=\lambda \left| \begin{matrix}    a & r & x  \\    b & s & y  \\    c & t & z  \\ \end{matrix} \right|\] Taking 2 common from \[{{R}_{2}}\] and \[-1\] from \[{{R}_{3}}\] in LHS \[\therefore -12\left| \begin{matrix}    a & r & x  \\    b & s & y  \\    c & t & z  \\ \end{matrix} \right|=\lambda \left| \begin{matrix}    a & r & x  \\    b & s & y  \\    c & t & z  \\ \end{matrix} \right|\] \[\Rightarrow \,\lambda =-12\]


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