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

  • question_answer
    \[\frac{d}{dx}\left( {{\tan }^{-1}}\sqrt{\frac{1+\cos \frac{x}{2}}{1-\cos \frac{x}{2}}} \right)\]is equal to [MP PET 2004]

    A)            \[-\frac{1}{4}\]

    B)            \[\frac{1}{2}\]

    C)            \[-\frac{1}{2}\]

    D)            \[\frac{1}{4}\]

    Correct Answer: A

    Solution :

               Let \[y={{\tan }^{-1}}\sqrt{\frac{1+\cos \frac{x}{2}}{1-\cos \frac{x}{2}}}={{\tan }^{-1}}\sqrt{\frac{2{{\cos }^{2}}\frac{x}{4}}{2{{\sin }^{2}}\frac{x}{4}}}\]                    \[y={{\tan }^{-1}}\cot \frac{x}{4}={{\tan }^{-1}}\tan \left( \frac{\pi }{2}-\frac{x}{4} \right)=\frac{\pi }{2}-\frac{x}{4}\]                    \ \[\frac{dy}{dx}=-\frac{1}{4}\].


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