CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2009

  • question_answer
    The derivative of\[{{\tan }^{-1}}\left( \frac{2x}{1-{{x}^{2}}} \right)\]with respect to\[{{\cos }^{-1}}\sqrt{1-{{x}^{2}}}\]is

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

    B)  \[\frac{1}{\sqrt{1-{{x}^{2}}}}\]

    C)  \[\frac{2}{\sqrt{1-{{x}^{2}}}(1+{{x}^{2}})}\]

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

    E)  \[\frac{2\sqrt{1-{{x}^{2}}}}{1+{{x}^{2}}}\]

    Correct Answer: E

    Solution :

    Let\[u={{\tan }^{-1}}\left( \frac{2x}{1-{{x}^{2}}} \right)\]and\[v={{\cos }^{-1}}\sqrt{1-{{x}^{2}}}\] On differentiating w.r.t. x respectively, we get \[\frac{du}{dx}=\frac{1}{1+{{\left( \frac{2x}{1-{{x}^{2}}} \right)}^{2}}}.\left[ \frac{{{(1-x)}^{2}}2-2x(-2x)}{{{(1-{{x}^{2}})}^{2}}} \right]\] \[=\frac{2+2{{x}^{2}}}{{{(1+{{x}^{2}})}^{2}}}=\frac{2}{1+{{x}^{2}}}\] and        \[\frac{dv}{dx}=-\frac{1}{\sqrt{1-(1-{{x}^{2}})}}.\left[ \frac{(-2x)}{2\sqrt{1-{{x}^{2}}}} \right]\]                 \[=\frac{1}{\sqrt{{{x}^{2}}}}\left[ \frac{x}{\sqrt{1-{{x}^{2}}}} \right]\]                 \[=\frac{1}{\sqrt{1-{{x}^{2}}}}\] \[\therefore \]  \[\frac{du}{dv}=\frac{\frac{2}{1+{{x}^{2}}}}{\frac{1}{\sqrt{1-{{x}^{2}}}}}=\frac{2\sqrt{1-{{x}^{2}}}}{1+{{x}^{2}}}\]             


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