JEE Main & Advanced JEE Main Paper (Held On 11-Jan-2019 Evening)

  • question_answer
    Let x, y be positive real numbers and m, n positive integers. The maximum value of the expression \[\frac{{{x}^{m}}{{y}^{n}}}{(1+{{x}^{2m}})(1+{{y}^{2n}})}\]is [JEE  Main Online Paper (Held on 11-jan-2019 Evening)]

    A) \[\frac{m+n}{6mn}\]                            

    B) 1

    C) 1/2                               

    D)   ¼

    Correct Answer: D

    Solution :

    Here, \[\frac{{{x}^{m}}{{y}^{n}}}{(1+{{x}^{2m}})(1+{{y}^{2n}})}=\frac{1}{\left( {{x}^{m}}+\frac{1}{{{x}^{m}}} \right)\left( {{x}^{n}}+\frac{1}{{{x}^{n}}} \right)}\] Now,\[{{x}^{m}}+\frac{1}{{{x}^{m}}}\ge 2\]and\[{{y}^{n}}+\frac{1}{{{y}^{n}}}\ge 2\] \[\therefore \]\[\frac{1}{\left( {{x}^{m}}+\frac{1}{{{x}^{m}}} \right)\left( {{y}^{n}}+\frac{1}{{{y}^{n}}} \right)}\le \frac{1}{4}\]


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