RAJASTHAN ­ PET Rajasthan PET Solved Paper-2002

  • question_answer
    The equation which has the roots\[\frac{1}{3+\sqrt{2}}\]and\[\frac{1}{3-\sqrt{2}}\]is

    A)  \[7{{x}^{2}}-6x+1=0\]

    B)  \[6{{x}^{2}}-7x+1=0\]

    C)  \[{{x}^{2}}-6x+7=0\]

    D)  \[{{x}^{2}}-7x+6=0\]

    Correct Answer: A

    Solution :

     Sum of roots\[=\frac{1}{3+\sqrt{2}}+\frac{1}{3-\sqrt{2}}\] \[=\frac{3-\sqrt{2}+3+\sqrt{2}}{{{3}^{2}}-{{(\sqrt{2})}^{2}}}\] \[=\frac{6}{7}\] and multiplication of roots\[=\frac{1}{3+\sqrt{2}}\times \frac{1}{3-\sqrt{2}}\] \[=\frac{1}{9-2}\] \[=\frac{1}{7}\] \[\therefore \]Required equation is \[{{x}^{2}}-\](sum of roots) \[x+\] (multiplication of roots)\[=0\] \[\Rightarrow \] \[{{x}^{2}}-\frac{6}{7}x+\frac{1}{7}=0\] \[\Rightarrow \] \[7{{x}^{2}}-6x+1=0\]


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