KVPY Sample Paper KVPY Stream-SX Model Paper-13

  • question_answer
    If \[f(x)\] is a function satisfying the relation \[{{x}^{2}}f(x)-2f\left( \frac{1}{x} \right)=g(x),\] where \[g\,(x)\] is odd function, then the value of \[f(2)\] is

    A) \[-f(2)\]

    B) \[-f(-\,2)\]

    C) \[f\left( \frac{1}{2} \right)\]

    D) \[-f\left( \frac{1}{2} \right)\]          

    Correct Answer: B

    Solution :

    We have, \[{{x}^{2}}f(x)-2f\left( \frac{1}{x} \right)=g\,(x),\]
    Where \[g(x)\] is odd function.
    \[\therefore \]\[g(x)+g(-x)=0\]
    \[{{x}^{2}}[f(x)+f(-x)]-2\left[ f\left( \frac{1}{x} \right)+f\left( -\frac{1}{x} \right) \right]=0\]
    \[x\to \frac{1}{x},\]we get \[\frac{1}{{{x}^{2}}}\left[ f\left( \frac{1}{x} \right)+f\left( -\frac{1}{x} \right)-2f(x)+f(-x) \right]=0\]
    From Eqs. (i) and (ii), we get
    \[f(x)=-f(-x)\]
    \[f(2)=-f(-\,2)\]


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