1. ## Sum of series-Geometric?

How do i show that

$\displaystyle \sum_{n=2}^{n}1/2^{n}\le0.5$

I know $\displaystyle \sum_{k=0}^{\infty}r^k=\frac{1}{1-r}$ but the above starts from n=2 so can't work it out.

thanks for any help.

2. Originally Posted by charikaar
How do i show that

$\displaystyle \sum_{n=2}^{n}1/2^{n}\le0.5$

I know $\displaystyle \sum_{k=0}^{\infty}r^k=\frac{1}{1-r}$ but the above starts from n=2 so can't work it out.

thanks for any help.
$\displaystyle \sum_{n=2}^{n}1/2^{n}=\sum_{j=0}^{n-2}1/2^{j+2}$