JCECE Engineering JCECE Engineering Solved Paper-2009

  • question_answer
    If\[\left| \begin{matrix}    x & {{x}^{2}} & 1+{{x}^{3}}  \\    y & {{y}^{2}} & 1+{{y}^{3}}  \\    z & {{z}^{2}} & 1+{{z}^{3}}  \\ \end{matrix} \right|=0\], then

    A) \[z=xy\]                              

    B) \[z=\frac{1}{xy}\]

    C) \[z=-\frac{1}{xy}\]                          

    D)  None of these

    Correct Answer: C

    Solution :

    Given that,                            \[\left| \begin{matrix}    x & {{x}^{2}} & 1+{{x}^{3}}  \\    y & {{y}^{2}} & 1+{{y}^{3}}  \\    z & {{z}^{2}} & 1+{{z}^{3}}  \\ \end{matrix} \right|=0\] \[\Rightarrow \]\[\left| \begin{matrix}    x & {{x}^{2}} & 1  \\    y & {{y}^{2}} & 1  \\    z & {{z}^{2}} & 1  \\ \end{matrix} \right|+xyz\left| \begin{matrix}    1 & x & {{x}^{2}}  \\    1 & y & {{y}^{2}}  \\    1 & z & {{z}^{2}}  \\ \end{matrix} \right|=0\] \[\Rightarrow \]          \[(1+xyz)=\left| \begin{matrix}    1 & x & {{x}^{2}}  \\    1 & y & {{y}^{2}}  \\    1 & z & {{z}^{2}}  \\ \end{matrix} \right|=0\] \[\Rightarrow \]                   \[xyz+1=0\Rightarrow z=-\frac{1}{xy}\]


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