BCECE Engineering BCECE Engineering Solved Paper-2003

  • question_answer
    \[\frac{d}{dx}\sqrt{\frac{1-\sin 2x}{1+\sin 2x}}\]is  equal to:

    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 :

    Let          \[y=\sqrt{\frac{1-\sin 2x}{1+\sin 2x}}\] \[=\sqrt{\frac{{{(\cos x-\sin x)}^{2}}}{{{(\cos x+\sin x)}^{2}}}}\] \[=\frac{1-\tan }{1+\tan x}\]                 \[\Rightarrow \]               \[y=\tan \left( \frac{\pi }{4}-x \right)\] On differentiating both sides w.r.t. \[x,\]we get \[\frac{dy}{dx}=-{{\sec }^{2}}\left( \frac{\pi }{4}-x \right)\]


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