# The sum of a series

1. Sep 23, 2012

2. Sep 23, 2012

### jbunniii

3. Sep 23, 2012

### damabo

you better use \frac{a}{b} to make clear what fraction you want to make.
make sure to use $[/itex ] (but without the latter space before the bracket) to place the expression you want between those two. 4. Sep 24, 2012 ### Ray Vickson You do it by finding the sum $$S(x) = \sum_{n=1}^{\infty} \frac{x^n}{n}$$ and then substituting the correct value of x. RGV 5. Sep 24, 2012 ### SammyS Staff Emeritus Yes, the wolframAlpha link confirms that it's the same problem. @Badmouton, The expression you are summing, with the proper set of parentheses: 2/(n*7n). This equivalent to (2*7-n)/n also equivalent to (2*(1/7)n)/n . All of these are more readable using LaTeX, which allows you to include the summation symbol, Ʃ , along with the summation limits. [itex]\displaystyle \sum_{n=1}^{\infty} \frac{2}{n7^{n}}$

$\displaystyle \sum_{n=1}^{\infty} \frac{2\left(7^{-n}\right)}{n}$

$\displaystyle \sum_{n=1}^{\infty} \frac{2\left(\frac{1}{7}\right)^{n}}{n}$