# Math Help - summation problem

1. ## summation problem

The problem is the summation of (n/(n+1)!) from n=1 to infinity.
any help that can be given is greatly appreciated!

2. Is...

$\displaystyle \frac{n}{(n+1)!}= \frac{n+1}{(n+1)!} - \frac{1}{(n+1)!}= \frac{1}{n!} - \frac{1}{(n+1)!}$ (1)

... so that...

$\displaystyle \sum_{n=1}^{\infty} \frac{n}{(n+1)!} = \sum_{n=1}^{\infty} \frac{1}{n!} - \sum_{n=1}^{\infty} \frac{1}{(n+1)!} = \sum_{n=1}^{\infty} \frac{1}{n!} - \sum_{n=2}^{\infty} \frac{1}{n!} = 1$ (2)

Kind regards

$\chi$ $\sigma$

3. sorry I have not done a summation in a long time but how do you know that the summation of 1/n! from one to infinity minus the summation of 1/n! from 2 to infinity is 1?
thanks so much for the help

4. Originally Posted by casey
sorry I have not done a summation in a long time but how do you know that the summation of 1/n! from one to infinity minus the summation of 1/n! from 2 to infinity is 1?
thanks so much for the help
Write out the first few terms and simplify.