CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2000

  • question_answer
    If \[f(x)=\frac{x-1}{x+1},\]then \[f(2x)\]is:

    A)  \[\frac{f(x)+1}{f(x)+3}\]                              

    B) \[\frac{3f(x)+1}{f(x)+3}\]

    C)  \[\frac{f(x)+3}{f(x)+1}\]                              

    D)  \[\frac{f(x+3)}{3f(x)+1}\]

    Correct Answer: B

    Solution :

    \[\frac{f(x)}{1}=\frac{x-1}{x+1}\] Applying componendo - dividend \[\frac{f(x)+1}{f(x)-1}=\frac{x-1+x+1}{x-1-x-1}=\frac{x}{-1}\] \[x=\frac{f(x)+1}{1-f(x)}\]                 Now      \[f(2x)=\frac{2x-1}{2x+1}\]                                 \[=\frac{2\left( \frac{f(x)+1}{1-f(x)} \right)-1}{2\left( \frac{f(x)+1}{1-f(x)} \right)+1}=\frac{3f(x)+1}{f(x)+3}\]


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