JCECE Engineering JCECE Engineering Solved Paper-2006

  • question_answer
    \[\int{\frac{dx}{x({{x}^{n}}+1)}}\]is equal to:

    A) \[\frac{1}{n}\log \left( \frac{{{x}^{n}}}{{{x}^{n}}+1} \right)+c\]

    B) \[\frac{1}{n}\log \left( \frac{{{x}^{n}}+1}{{{x}^{n}}} \right)+c\]

    C) \[\log \left( \frac{{{x}^{n}}}{{{x}^{n}}+1} \right)+c\]

    D)  none of the above

    Correct Answer: A

    Solution :

    Let\[\int{\frac{dx}{x({{x}^{n}}+1)}}\]  Putting    \[{{x}^{n}}+1=t\] \[\Rightarrow \]               \[n{{x}^{n-1}}dx=dt\] \[\therefore \]            \[I=\frac{1}{n}\int{\frac{dt}{t(t-1)}}\]                              \[=\frac{1}{n}\int{\left( \frac{1}{t-1}-\frac{1}{t} \right)dt}\]                              \[=\frac{1}{n}\log \left( \frac{t-1}{t} \right)+c\]                              \[=\frac{1}{n}\log \left( \frac{{{x}^{n}}}{{{x}^{n}}+1} \right)+c\]


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