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

  • question_answer
     If \[y=\sqrt{\frac{1+\tan x}{1-\tan x}}\], then \[\frac{dy}{dx}=\] [AISSE 1981, 83, 84, 85; DSSE 1985; AI CBSE 1981, 83]

    A)          \[\frac{1}{2}\sqrt{\frac{1-\tan x}{1+\tan x}}.{{\sec }^{2}}\left( \frac{\pi }{4}+x \right)\]

    B)            \[\sqrt{\frac{1-\tan x}{1+\tan x}}.{{\sec }^{2}}\left( \frac{\pi }{4}+x \right)\]

    C)            \[\frac{1}{2}\sqrt{\frac{1-\tan x}{1+\tan x}}.\sec \left( \frac{\pi }{4}+x \right)\]

    D)            None of these

    Correct Answer: A

    Solution :

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


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