KVPY Sample Paper KVPY Stream-SX Model Paper-23

  • question_answer
    Let \[f:(0,1)\]\[\to \]\[R\] be defined by \[f(x)=\frac{b-x}{1-bx},\] where b is constant such that \[0<b<1.\]Then,

    A) \[f\]is not invertible in (0, 1)                   

    B) \[f\ne {{f}^{-1}}\]on \[(0,1)\]and \[f'(b)=\frac{1}{f(0)}\]

    C) \[f={{f}^{-\,1}}\]on \[(0,1)\]and \[f'(b)=\frac{1}{f'(0)}\]

    D) \[{{f}^{-\,1}}\]is differentiable in (0, 1)

    Correct Answer: A

    Solution :

    We have, \[f\left( x \right)=\frac{b-x}{1-bx},x\in \left( 0,1 \right)\,\] and \[b\in \left( 0,1 \right)\]
    Let \[f\left( x \right)=y\]
    \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,y=\frac{b-x}{1-bx}\]  \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,y-ybx=b-x\]            \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,x=\frac{b-y}{1-by}\]
    Range \[f\left( x \right)\ne R\]
    \[\therefore \,\,\,\,\,\,\,\,\,\,\,\,\,f(x)\] is not invertible in (0, 1).


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