JEE Main & Advanced Mathematics Functions Question Bank Functions

  • question_answer
    The inverse of the function \[f(x)=\frac{{{e}^{x}}-{{e}^{-x}}}{{{e}^{x}}+{{e}^{-x}}}+2\] is given by [Kurukshetra CEE 1996]

    A)                    \[{{\log }_{e}}{{\left( \frac{x-2}{x-1} \right)}^{1/2}}\]

    B)            \[{{\log }_{e}}{{\left( \frac{x-1}{3-x} \right)}^{1/2}}\]

    C)                    \[{{\log }_{e}}{{\left( \frac{x}{2-x} \right)}^{1/2}}\]

    D)            \[{{\log }_{e}}{{\left( \frac{x-1}{x+1} \right)}^{-2}}\]

    Correct Answer: B

    Solution :

               \[y=\frac{{{e}^{x}}-{{e}^{-x}}}{{{e}^{x}}+{{e}^{-x}}}+2\,\,\Rightarrow \,\,y=\frac{{{e}^{2x}}-1}{{{e}^{2x}}+1}+2\,\,\]                    \[\Rightarrow \,\,{{e}^{2x}}=\frac{1-y}{y-3}=\frac{y-1}{3-y}\,\,\Rightarrow \,\,x=\frac{1}{2}{{\log }_{e}}\,\left( \frac{y-1}{3-y} \right)\]                    \[\Rightarrow {{f}^{-1}}(y)={{\log }_{e}}\,{{\left( \frac{y-1}{3-y} \right)}^{1/2}}\Rightarrow {{f}^{-1}}(x)={{\log }_{e}}{{\left( \frac{x-1}{3-x} \right)}^{1/2}}\].


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