JCECE Engineering JCECE Engineering Solved Paper-2013

  • question_answer
    If\[y={{\sin }^{-1}}\left( \frac{2x}{1+{{x}^{2}}} \right)+{{\sec }^{-1}}\left( \frac{1+{{x}^{2}}}{1-{{x}^{2}}} \right)\], then\[\frac{dy}{dx}\] is equal to

    A) \[\frac{7}{1+{{x}^{2}}}\]                               

    B) \[\frac{4}{1+{{x}^{2}}}\]

    C) \[\frac{1}{x}\]                                   

    D)  None of these

    Correct Answer: A

    Solution :

    We have,                 \[y={{\sin }^{-1}}\left( \frac{2x}{1+{{x}^{2}}} \right)+{{\sec }^{-1}}\left( \frac{1+{{x}^{2}}}{1-{{x}^{2}}} \right)\] Let\[x=\tan \theta \] Then,\[y={{\sin }^{-1}}\left( \frac{2\tan \theta }{1+{{\tan }^{2}}\theta } \right)+{{\sec }^{-1}}\left( \frac{1+{{\tan }^{2}}\theta }{1-{{\tan }^{2}}\theta } \right)\]                       \[=2\theta +2\theta =4{{\tan }^{-1}}x\] \[\therefore \]  \[\frac{dy}{dx}=\frac{4}{1+{{x}^{2}}}\]


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