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

  • question_answer
    The value of \[\frac{2\frac{1}{2}}{1\,!}+\frac{3\frac{1}{2}}{2\,!}+\frac{4\frac{1}{2}}{3\,!}+\frac{5\frac{1}{2}}{4\,!}+......\infty \] is

    A) \[1+e\]

    B) \[\frac{1+e}{e}\]

    C) \[\frac{e-1}{e}\]

    D) None of these

    Correct Answer: D

    Solution :

    The series is  \[\frac{\left( 2+\frac{1}{2} \right)}{1!}+\frac{\left( 3+\frac{1}{2} \right)}{2!}+......\infty \]     \[=\left\{ \frac{2}{1!}+\frac{3}{2!}+....+\frac{n+1}{n!}+....\infty  \right\}+\]\[\frac{1}{2}\left\{ \frac{1}{1!}+\frac{1}{2!}+....\frac{1}{n!}+...\infty  \right\}\]     \[=e+(e-1)+\frac{1}{2}(e-1)=\frac{5e}{2}-\frac{3}{2}\].


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