Posted by **Robo123** on Saturday, December 11, 2010 at 10:24am.

Find the sum of the geometric series 128 - 64 + 32 - . . . to 8 terms.

a) 85

b) 225

c) 86

d) 85/2

e) not possible

- Math - Geometric Series -
**Reiny**, Saturday, December 11, 2010 at 10:47am
r = -64/128 = -1/2

a = 128

sum(8) = 128( 1 - (1/2)^8 / (1+1/2)

= 128(255/256)(2/3) = 85

- Math - Geometric Series -
**drwls**, Saturday, December 11, 2010 at 10:57am
With only 8 terms, it's easier for me to do the addition than remember the formula.

Adding in pairs, successive pairs are lower by a factor of 4.

64 + 16 + 4 + 1 = 85

- Math - Geometric Series -
**sylow theorems**, Sunday, December 12, 2010 at 10:08pm
128-64+32-16+8-4+2-1=64+16+4+1=80+5=85(!)

## Answer This Question

## Related Questions

- sum geometric series - what is the sum of geometric infinite series 3/2+ 9/16+ ...
- CALC II - Determine the convergence of the following series using the nth-...
- MATH - the fist term of a geometric series is 1, the nth term is 128 and the sum...
- Pre-Calculus - Q.Determine the sum of each infinite geometric series. t_1= 8 r...
- Geometric Series (Algebra 2) - I need some assistance or a formula when trying ...
- Math/Pre Cal - Find the sum of the geometric series 128-64+32-______to 8 terms .
- Math/Pre Cal - Find the sum of the geometric series 128-64+32-______to 8 terms .
- algebra - Can someone please help me with this problem? Thanks! Evaluate the ...
- math studies - An arithmetic series has a first term of -4 and a common ...
- math - sorry for before it is my first time using this website and this is the ...

More Related Questions