CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2009

  • question_answer
    If\[1,\omega ,{{\omega }^{2}}\]are the cube roots of unity and if\[\left[ \begin{matrix}    1+\omega  & 2\omega   \\    -2\omega  & -b  \\ \end{matrix} \right]+\left[ \begin{matrix}    a & -\omega   \\    3\omega  & 2  \\ \end{matrix} \right]=\left[ \begin{matrix}    0 & \omega   \\    \omega  & 1  \\ \end{matrix} \right],\] then\[{{a}^{2}}+{{b}^{2}}\]is equal to

    A)  \[1+{{\omega }^{2}}\]                  

    B)  \[{{\omega }^{2}}-1\]

    C)  \[1+\omega \] 

    D)         \[{{(1+\omega )}^{2}}\]

    E)  \[{{\omega }^{2}}\]

    Correct Answer: C

    Solution :

    Given, \[\left[ \begin{matrix}    1+\omega  & 2\omega   \\    -2\omega  & -b  \\ \end{matrix} \right]+\left[ \begin{matrix}    a & -\omega   \\    3\omega  & 2  \\ \end{matrix} \right]=\left[ \begin{matrix}    0 & \omega   \\    \omega  & 1  \\ \end{matrix} \right]\] \[\Rightarrow \]               \[\left[ \begin{matrix}    1+\omega +a & \omega   \\    \omega  & 2-b  \\ \end{matrix} \right]=\left[ \begin{matrix}    0 & \omega   \\    \omega  & 1  \\ \end{matrix} \right]\] \[\Rightarrow \]               \[1+\omega +a=0,2-b=1\] \[\Rightarrow \]               \[a=-1-\omega ,b=1\] \[\therefore \]  \[{{a}^{2}}+{{b}^{2}}=(-1-{{\omega }^{2}})+{{1}^{2}}\]                 \[=1+{{\omega }^{2}}+2\omega +{{1}^{2}}\]                 \[=0+\omega +1\]           \[(\because 1+\omega +{{\omega }^{2}}=0)\]                 \[=1+\omega \]


You need to login to perform this action.
You will be redirected in 3 sec spinner