11th Class Mathematics Sample Paper Mathematics Olympiad - Sample Paper-8

  • question_answer
    If \[f(x)=\frac{\mathbf{3x}+\mathbf{1}}{\mathbf{5x}-\mathbf{3}}\].then

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

    B)  \[f\,of\left( x \right)=f\left( x \right)\]

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

    D)  \[{{f}^{-1}}(x)=\frac{1}{20}f(x)\]

    Correct Answer: C

    Solution :

    [c] \[\because f(x)=\frac{3x+1}{5x-3}\Rightarrow \,y=\frac{3x+2}{5x-3}\] \[5y.x-3y=3x+2x\left( 5y-3 \right)=3y+2\] \[x=\frac{3y+2}{5y-3}.\,\,\]  \[\therefore Hence\,{{f}^{-1}}(x)=f(x).\] Option [c] is correct.


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