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

  • question_answer
    \[\frac{1}{1\,.\,3}+\frac{1}{2}\,.\,\frac{1}{3\,.\,5}+\frac{1}{3}\,.\,\frac{1}{5\,.\,7}+......\infty =\]

    A) \[2\,{{\log }_{e}}2-1\]

    B) \[{{\log }_{e}}2-1\]

    C) \[{{\log }_{e}}2\]

    D) None of these

    Correct Answer: A

    Solution :

    \[S=\frac{1}{2}\left( \frac{1}{1}-\frac{1}{3} \right)+\frac{1}{{{2}^{2}}}\left( \frac{1}{3}-\frac{1}{5} \right)+....\] \[=\left( \frac{1}{1.2}-\frac{1}{2.3} \right)+\left( \frac{1}{3.4}-\frac{1}{4.5} \right)+....=2{{\log }_{e}}2-1\] .


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