JEE Main & Advanced Sample Paper JEE Main Sample Paper-4

  • question_answer
    The number of positive integral solutions of the equation \[\left| \begin{matrix}    {{x}^{3}}+1 & {{x}^{2}}y & {{x}^{2}}z  \\    x{{y}^{2}} & {{y}^{3}}+1 & {{y}^{2}}z  \\    x{{z}^{2}} & y{{z}^{2}} & {{z}^{3}}+1  \\ \end{matrix} \right|=11\]is

    A)  0                            

    B)  3      

    C)  6                            

    D)  12

    Correct Answer: B

    Solution :

    \[\frac{1}{xyz}\left| \begin{matrix}    {{x}^{4}}+x & {{x}^{3}}y & {{x}^{3}}z  \\    x{{y}^{3}} & {{y}^{4}}+y & {{y}^{3}}z  \\    x{{z}^{3}} & y{{z}^{3}} & {{z}^{4}}+z  \\ \end{matrix} \right|=11\] \[\frac{xyz}{xyz}\left| \begin{matrix}    {{x}^{3}}+1 & {{x}^{3}} & {{x}^{3}}  \\    {{y}^{3}} & {{y}^{3}}+1 & {{y}^{3}}  \\    {{z}^{3}} & {{z}^{3}} & {{z}^{3}}+1  \\ \end{matrix} \right|=11\] use\[{{R}_{1}}\to {{R}_{1}}+{{R}_{2}}+{{R}_{3}}\] \[D=({{x}^{3}}+{{y}^{3}}+{{z}^{3}}+1)\]\[\left| \begin{matrix}    1 & 1 & 1  \\    {{y}^{3}} & {{y}^{3}}+1 & {{y}^{3}}  \\    {{z}^{3}} & {{z}^{3}} & {{z}^{3}}+1  \\ \end{matrix} \right|=11\] Hence,\[{{x}^{3}}+{{y}^{3}}+{{z}^{3}}=10\] \[(2,1,1),(1,2,1),(1,1,2)\]


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