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

  • question_answer
    If \[y={{\cot }^{-1}}\left[ \frac{\sqrt{1+\sin x}+\sqrt{1-\sin x}}{\sqrt{1+\sin x}-\sqrt{1-\sin x}} \right]\], then \[\frac{dy}{dx}=\]

    A)  \[\frac{1}{2}\]

    B)            \[\frac{2}{3}\]

    C)            3

    D)            1

    Correct Answer: A

    Solution :

               \[y={{\cot }^{-1}}\left[ \frac{\sqrt{1+\sin x}+\sqrt{1-\sin x}}{\sqrt{1+\sin x}-\sqrt{1-\sin x}} \right]\]                      \[={{\cot }^{-1}}\left[ \frac{2+2\cos x}{2\sin x} \right]={{\cot }^{-1}}\left[ \frac{1+\cos x}{\sin x} \right]\]                      \[={{\cot }^{-1}}\left[ \cot \frac{x}{2} \right]=\frac{x}{2}\]                    \[\therefore \frac{dy}{dx}=\frac{1}{2}\] .


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