# Geometric Series Problem Help

1. Jul 14, 2008

### ssjSolidSnake

Hi, I'm having trouble finding the sequence's total sum from a formula concerning Geometric Series.
I've been using a calculator to find and manually input all of the terms into a table in Microsoft Excel and adding them all up at the end. The formula that I was given was $$\overline{10}\sum\underline{1}$$4(1/2)^n-1

The total sum that I found was 7.992188, but it was incorrect.

Can anyone help me find the Series Sum?

Last edited: Jul 14, 2008
2. Jul 14, 2008

### CompuChip

Can you express the question a little more precisely? I can't make sense of the overline 10, the underline 1, and where the rest of the formula is supposed to go. Please either use proper TeX code, or don't use it at all and write it out clearly and unambiguously. For example,
$$10 \sum_{n = 0}^\infty \frac{1}{4} \left( \frac{1}{2} \right)^{n - 1}$$
or
10 * (sum from n = 0 to infinity)[ (1/4) (1/2)^(n - 1) ]

3. Jul 14, 2008

### ssjSolidSnake

Sorry about that. I'm not familiar with LaTex so I will attempt to state my problem as clearly as possible. (sum from n=1 to 10) [ 4(1/2)^(n - 1) ]

4. Jul 14, 2008

### mathman

It looks like you have a finite geometric series.

sum(0,N) an = (1-aN+1)/(1-a)

You should be able to do the rest

5. Jul 14, 2008

### Staff: Mentor

https://www.physicsforums.com/misc/howtolatex.pdf

\sum _{n=1} ^{10} 4 (\frac 1 2)^{n-1}

$$\sum _{n=1} ^{10} 4 (\frac 1 2)^{n-1}$$

Click on the generated formula to see LaTeX code used.