CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2007

  • question_answer
    If \[{{\sec }^{-1}}\left( \frac{1+x}{1-y} \right)=a,\]then \[\frac{dy}{dx}\] is

    A)  \[\frac{y-1}{x+1}\]                         

    B)  \[\frac{y+1}{x-1}\]

    C)  \[\frac{x-1}{y-1}\]                          

    D)  \[\frac{x-1}{y+1}\]

    Correct Answer: A

    Solution :

    Given,  \[{{\sec }^{-1}}\left( \frac{1+x}{1-y} \right)=a\] \[\Rightarrow \]               \[\frac{1+x}{1-y}=\sec a\] \[\Rightarrow \]               \[1+x=(1-y)\sec a\] \[\Rightarrow \]               \[y\,\sec \,a=\sec \,a-1-x\] \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{-1}{\sec \,a}=\frac{-1}{\left( \frac{1+x}{1-y} \right)}\] \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{-(1-y)}{(1+x)}\] \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{1-y}{1+x}\]


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