JEE Main & Advanced JEE Main Paper (Held On 8 April 2017)

  • question_answer
    If the arithmetic mean of two numbers and b,a, > b > 0. Is five times their geometric mean, then\[\frac{a+b}{a-b}\]is equal to:   [JEE Online 08-04-2017]

    A) \[\frac{7\sqrt{3}}{12}\]                                 

    B) \[\frac{3\sqrt{2}}{4}\]

    C) \[\frac{\sqrt{6}}{2}\]                                     

    D) \[\frac{5\sqrt{6}}{12}\]

    Correct Answer: D

    Solution :

                                    \[\frac{a+b}{2}=5\sqrt{ab}\]                                 \[\frac{a+b}{\sqrt{ab}}=10\]                 \[\therefore \]  \[\frac{a}{b}=\frac{10+\sqrt{96}}{10-\sqrt{96}}=\frac{10+4\sqrt{6}}{10-4\sqrt{6}}\]                 Use C and D                 \[\frac{a+b}{a-b}=\frac{20}{8\sqrt{6}}=\frac{5}{2\sqrt{6}}=\frac{5\sqrt{6}}{12}\]


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