RAJASTHAN ­ PET Rajasthan PET Solved Paper-2008

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


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