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

  • question_answer
    \[\frac{d}{dx}\log \tan \left( \frac{\pi }{4}+\frac{x}{2} \right)=\]

    A)            \[\cos \text{ec}\,x\]

    B)            \[-\cos \text{ec}\,x\]

    C)            \[\sec x\]

    D)            \[-\sec x\]

    Correct Answer: C

    Solution :

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


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