CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2005

  • question_answer
    If\[f(x)=\left| \begin{matrix}    x-3 & 2{{x}^{2}}-18 & 3{{x}^{3}}-81  \\    x-5 & 2{{x}^{2}}-50 & 4{{x}^{3}}-500  \\    1 & 2 & 3  \\ \end{matrix} \right|,\]then\[f(1).f(3)+f(3).f(5)+f(5).f(1)\]is equal to:

    A)  \[f(1)\]               

    B)  \[f(3)\]

    C)  \[f(1)+f(3)\]     

    D)         \[f(1)+f(5)\]

    E)  \[f(1)+f(3)+f(5)\]           

    Correct Answer: B

    Solution :

    \[\because \] \[f(1)=\left| \begin{matrix}    -2 & -16 & -78  \\    -4 & -48 & 496  \\    1 & 2 & 3  \\ \end{matrix} \right|\] \[f(3)=\left| \begin{matrix}    0 & 0 & 0  \\    -2 & -32 & -392  \\    1 & 2 & 3  \\ \end{matrix} \right|=0\] and        \[f(5)=\left| \begin{matrix}    2 & 32 & 294  \\    0 & 0 & 0  \\    1 & 2 & 3  \\ \end{matrix} \right|=0\] \[\therefore \] \[f(1).f(3)+f(3)-f(5)+f(5).f(1)\]                 \[=f(1).0+0+f(1).0\]                 \[=0=f(3)\]


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