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

  • question_answer
    \[\frac{d}{dx}\sqrt{\frac{1-\sin 2x}{1+\sin 2x}}=\]     [AISSE 1985; DSSE 1986]

    A)            \[{{\sec }^{2}}x\]

    B) \[-{{\sec }^{2}}\left( \frac{\pi }{4}-x \right)\]

    C)            \[{{\sec }^{2}}\left( \frac{\pi }{4}+x \right)\]

    D)            \[{{\sec }^{2}}\left( \frac{\pi }{4}-x \right)\]

    Correct Answer: B

    Solution :

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


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