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

  • question_answer
    \[\frac{m-n}{m+n}+\frac{1}{3}{{\left( \frac{m-n}{m+n} \right)}^{3}}+\frac{1}{5}{{\left( \frac{m-n}{m+n} \right)}^{5}}+......\infty =\]

    A) \[{{\log }_{e}}\left( \frac{m}{n} \right)\]

    B) \[{{\log }_{e}}\left( \frac{n}{m} \right)\]

    C)  \[{{\log }_{e}}\left( \frac{m-n}{m+n} \right)\]

    D) \[\frac{1}{2}{{\log }_{e}}\left( \frac{m}{n} \right)\]

    Correct Answer: D

    Solution :

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


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