JEE Main & Advanced JEE Main Solved Paper-2016

  • question_answer
    If\[f(x)+2f\left( \frac{1}{x} \right)=3x,x\ne 0,\]and \[S=\{x\in R;f(x)=f(-x)\};\]then [JEE Main Solved Paper-2016 ]

    A) contains more than two elements.

    B)  is an empty set.

    C) contains exactly one element

    D) contains exactly two elements

    Correct Answer: D

    Solution :

                    \[f(x)+2f(1/x)=3x\]                                         .... (1) \[x\to \frac{1}{x}\Rightarrow f(1/x)+2f(x)=3/x\]               ?(2) \[f(x)+2\left( \frac{3}{x}-2f(x) \right)=3x\] \[\Rightarrow 3f(x)=\frac{6}{x}-3x\] \[\Rightarrow f(x)=\frac{2}{x}-x\] For S \[f(x)=f(-x)\Rightarrow \frac{2}{x}-x=0\] \[\Rightarrow x=\pm \sqrt{2}\]


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