JEE Main & Advanced Mathematics Functions Question Bank Functions

  • question_answer
    Which of the following functions is inverse of itself

    A)                    \[f(x)=\frac{1-x}{1+x}\]

    B)            \[f(x)={{5}^{\log x}}\]

    C)                    \[f(x)={{2}^{x(x-1)}}\]

    D)            None of these

    Correct Answer: A

    Solution :

               Since \[fof(x)=f\,(f(x)\,)=f\left( \frac{1-x}{1+x} \right)=\frac{1-\frac{1-x}{1+x}}{1+\frac{1-x}{1+x}}=x,\,\forall x\]                    \[\therefore \,\,\,fof=I\,\Rightarrow \,\,f\] is the inverse of itself.


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