RAJASTHAN ­ PET Rajasthan PET Solved Paper-2001

  • question_answer
    If\[f(x)={{x}^{2}}+1,\] then the value of\[{{f}^{-1}}(17)\]and\[{{f}^{-1}}(-3)\]are respectively

    A)  4, 1              

    B)  4, 0

    C)  3, 2              

    D)  None of these

    Correct Answer: D

    Solution :

     Let \[y={{x}^{2}}+1\] \[\Rightarrow \] \[{{x}^{2}}=y-1\] \[\Rightarrow \] \[x=\pm \sqrt{y-1}\] \[\Rightarrow \] \[{{f}^{-1}}(y)=\pm \sqrt{y-1}\] \[\Rightarrow \] \[{{f}^{-1}}(x)=\pm \sqrt{x-1}\] \[\therefore \] \[{{f}^{-1}}(17)=\pm \sqrt{17-1}=\pm 4\] and \[{{f}^{-1}}(-3)=\pm \sqrt{-3-1}\] \[=\pm \sqrt{-4},\] which is not possible. Alternate Method : Since\[f(x)\]is an even function, so its inverse cannot be defined.


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