JEE Main & Advanced Mathematics Differentiation Question Bank Derivative at a point Standard Differentiation

  • question_answer
    If \[y={{\sec }^{-1}}\left( \frac{\sqrt{x}+1}{\sqrt{x}-1} \right)+{{\sin }^{-1}}\left( \frac{\sqrt{x}-1}{\sqrt{x}+1} \right)\], then \[\frac{dy}{dx}=\] [UPSEAT 1999; AMU 2002; Kerala (Engg.) 2005]

    A)            0

    B)            \[\frac{1}{\sqrt{x}+1}\]

    C)            1

    D)            None of these

    Correct Answer: A

    Solution :

               \[y={{\sec }^{-1}}\left( \frac{\sqrt{x}+1}{\sqrt{x}-1} \right)+{{\sin }^{-1}}\left( \frac{\sqrt{x}-1}{\sqrt{x}+1} \right)\]                      \[={{\cos }^{-1}}\left( \frac{\sqrt{x}-1}{\sqrt{x}+1} \right)+{{\sin }^{-1}}\left( \frac{\sqrt{x}-1}{\sqrt{x}+1} \right)=\frac{\pi }{2}\]                    Þ \[\frac{dy}{dx}=0\] ,    \[\left\{ \because {{\sin }^{-1}}x+{{\cos }^{-1}}x=\frac{\pi }{2} \right\}\].


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