JEE Main & Advanced Mathematics Sequence & Series Question Bank Logarithmic series

  • question_answer
    \[\frac{1}{x+1}+\frac{1}{2\,{{(x+1)}^{2}}}+\frac{1}{3\,{{(x+1)}^{3}}}+....\infty =\]

    A)  \[{{\log }_{e}}\left( 1+\frac{1}{x} \right)\]

    B) \[{{\log }_{e}}\left( 1-\frac{1}{x} \right)\]

    C) \[{{\log }_{e}}\left( \frac{x}{x+1} \right)\]

    D) None of these

    Correct Answer: A

    Solution :

    Given series is \[\frac{1}{x+1}+\frac{1}{2{{(x+1)}^{2}}}+\frac{1}{3{{(x+1)}^{3}}}+.......\infty \] \[=-{{\log }_{e}}\left( 1-\frac{1}{x+1} \right)=-{{\log }_{e}}\left( \frac{x}{x+1} \right)\] \[={{\log }_{e}}\left( \frac{x+1}{x} \right)={{\log }_{e}}\left( 1+\frac{1}{x} \right)\].


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