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

  • question_answer
    \[\frac{d}{dx}\left( {{\tan }^{-1}}\frac{\cos x}{1+\sin x} \right)=\] [AISSE 1984, 85; MNR 1983; RPET 1997]

    A)            \[-\frac{1}{2}\]

    B)            \[\frac{1}{2}\]

    C)            \[-1\]

    D)            1

    Correct Answer: A

    Solution :

               \[\frac{d}{dx}\left[ {{\tan }^{-1}}\left( \frac{\cos x}{1+\sin x} \right) \right]\]            \[=\frac{d}{dx}\left[ {{\tan }^{-1}}\left( \frac{{{\cos }^{2}}\frac{x}{2}-{{\sin }^{2}}\frac{x}{2}}{{{\cos }^{2}}\frac{x}{2}+{{\sin }^{2}}\frac{x}{2}+2\sin \frac{x}{2}\cos \frac{x}{2}} \right) \right]\]            \[=\frac{d}{dx}\left[ {{\tan }^{-1}}\left( \frac{1-\tan \left( \frac{x}{2} \right)}{1+\tan \left( \frac{x}{2} \right)} \right) \right]=\frac{d}{dx}\left[ {{\tan }^{-1}}\tan \left( \frac{\pi }{4}-\frac{x}{2} \right) \right]=-\frac{1}{2}\]


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