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

  • question_answer
    \[{{\log }_{e}}x-{{\log }_{e}}(x-1)=\]

    A) \[\frac{1}{x}-\frac{1}{2{{x}^{2}}}+\frac{1}{3{{x}^{3}}}-.....\infty \]

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

    C) \[2\,\left( \frac{1}{x}+\frac{1}{3{{x}^{3}}}+\frac{1}{5{{x}^{5}}}+...\infty  \right)\]

    D)  \[2\,\left( \frac{1}{x}-\frac{1}{3{{x}^{3}}}+\frac{1}{5{{x}^{5}}}-...\infty  \right)\]

    Correct Answer: B

    Solution :

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


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