RAJASTHAN ­ PET Rajasthan PET Solved Paper-2003

  • question_answer
    If\[\omega \]is the cube root of unity, then the value of \[\left| \begin{matrix}    1 & \omega  & {{\omega }^{2}}  \\    \omega  & {{\omega }^{2}} & 1  \\    {{\omega }^{2}} & 1 & \omega   \\ \end{matrix} \right|\]is equal to

    A)  1                   

    B)  0

    C)  \[\omega \]                    

    D)  \[{{\omega }^{2}}+1\]

    Correct Answer: B

    Solution :

     \[\left| \begin{matrix}    1 & \omega  & {{\omega }^{2}}  \\    \omega  & {{\omega }^{2}} & 1  \\    {{\omega }^{2}} & 1 & \omega   \\ \end{matrix} \right|=\left| \begin{matrix}    1+\omega +{{\omega }^{2}} & \omega  & {{\omega }^{2}}  \\    \omega +{{\omega }^{2}}+1 & {{\omega }^{2}} & 1  \\    {{\omega }^{2}}+1+\omega  & 1 & \omega   \\ \end{matrix} \right|\] \[[{{C}_{1}}\to {{C}_{1}}+{{C}_{2}}+{{C}_{3}}]\] \[=\left| \begin{matrix}    0 & \omega  & {{\omega }^{2}}  \\    0 & {{\omega }^{2}} & 1  \\    0 & 1 & \omega   \\ \end{matrix} \right|\]\[[\because 1+\omega +{{\omega }^{2}}=0]\] \[=0\]


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