CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2009

  • question_answer
    If \[\frac{d}{dx}\{f(x)\}=\frac{1}{1+{{x}^{2}}},\]then\[\frac{d}{dx}\{f({{x}^{3}})\}\]is equal to

    A)  \[\frac{3x}{1+{{x}^{3}}}\]                           

    B)  \[\frac{3{{x}^{2}}}{1+{{x}^{6}}}\]

    C)  \[\frac{-6{{x}^{5}}}{{{(1+{{x}^{6}})}^{2}}}\]        

    D)         \[\frac{-6{{x}^{5}}}{1+{{x}^{6}}}\]

    E)  \[{{\tan }^{-1}}x\]

    Correct Answer: B

    Solution :

    Given, \[\frac{d}{dx}\{f(x)\}=\frac{1}{1+{{x}^{2}}}\] On integrating both sides, we get                 \[f(x)={{\tan }^{-1}}x\] \[\therefore \]  \[\frac{d}{dx}=f{{(x)}^{3}}=\frac{d}{dx}({{\tan }^{-1}}{{x}^{3}})\]                 \[=\frac{1}{1+{{({{x}^{3}})}^{2}}}.3{{x}^{2}}\]                 \[=\frac{3{{x}^{2}}}{1+{{x}^{6}}}\]


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