Manipal Engineering Manipal Engineering Solved Paper-2013

  • question_answer
    Let\[{{\alpha }_{1}},\,\,{{\alpha }_{2}}\]and\[{{\beta }_{1}},\,\,{{\beta }_{2}}\]be the roots of\[a{{x}^{2}}+bx+c=0\]and\[p{{x}^{2}}+qx+r=0\]respectively. If the system of equations\[{{\alpha }_{1}}y+{{\alpha }_{2}}z=0\]and\[{{\beta }_{1}}y+{{\beta }_{2}}z=0\]has  a non-trivial solution, then

    A) \[{{b}^{2}}pr={{q}^{2}}ac\]                         

    B) \[bp{{r}^{2}}=qa{{c}^{2}}\]

    C) \[b{{p}^{2}}r=q{{a}^{2}}c\]         

    D)         None of these

    Correct Answer: A

    Solution :

    Given system has non-trivial solution then                 \[\left| \begin{matrix}    {{\alpha }_{1}} & {{\alpha }_{2}}  \\    {{\beta }_{1}} & {{\beta }_{2}}  \\ \end{matrix} \right|=0\] \[\Rightarrow \]               \[{{\alpha }_{1}}{{\beta }_{2}}={{\alpha }_{2}}{{\beta }_{1}}\] \[\Rightarrow \]               \[\frac{{{\alpha }_{1}}}{{{\beta }_{1}}}=\frac{{{\alpha }_{2}}}{{{\beta }_{2}}}=\frac{{{\alpha }_{1}}+{{\alpha }_{2}}}{{{\beta }_{1}}+{{\beta }_{2}}}=\sqrt{\frac{{{\alpha }_{1}}{{\alpha }_{2}}}{{{\beta }_{1}}{{\beta }_{2}}}}\] \[\Rightarrow \]               \[\frac{-b/a}{-q/p}=\sqrt{\frac{c/a}{r/p}}\] \[\Rightarrow \]               \[\frac{bp}{aq}=\sqrt{\frac{cp}{ar}}\] \[\Rightarrow \]               \[{{b}^{2}}{{p}^{2}}ar={{a}^{2}}{{q}^{2}}cp\] \[\Rightarrow \]               \[{{b}^{2}}pr={{q}^{2}}ac\]


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