Math - Geometric Series

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

  1. 👍 0
  2. 👎 0
  3. 👁 389
  1. r = -64/128 = -1/2
    a = 128

    sum(8) = 128( 1 - (1/2)^8 / (1+1/2)
    = 128(255/256)(2/3) = 85

    1. 👍 0
    2. 👎 0
    posted by Reiny
  2. 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

    1. 👍 0
    2. 👎 0
    posted by drwls
  3. 128-64+32-16+8-4+2-1=64+16+4+1=80+5=85(!)

    1. 👍 0
    2. 👎 0

Respond to this Question

First Name

Your Response

Similar Questions

  1. Math/Pre Cal

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

    asked by Robo123 on December 10, 2010
  2. Math/Pre Cal

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

    asked by Robo123 on December 10, 2010
  3. CALC II

    Determine the convergence of the following series using the nth-partial sum or geometric series formula. The sum of n=1 to inifitiy 1/(9n^2+3n-2) How do I start? I'm guessing I should factor out the denominator but whats after

    asked by Ace on June 18, 2007
  4. Pre-Calculus

    Q.Determine the sum of each infinite geometric series. t_1= 8 r = -2^1/2 ---------------------------------------- A.This is a divergent series because the absolute value of r is greater than 1.

    asked by Lucina on February 17, 2015
  5. sum geometric series

    what is the sum of geometric infinite series 3/2+ 9/16+ 27/128+ 81/1024=.... i know the formula is S=a/(1-r) my teacher, he usually transforms into a formula of the sum series and finds out a and r.but i don't how to do that. the

    asked by david on April 9, 2007
  6. Algebra

    Use the geometric sequence of numbers 1, 1/3, 1/9, 1/27… to find the following: Using the formula for the sum of the first n terms of a geometric series, what is the sum of the first 10 terms? Carry all calculations to 6

    asked by Gina on October 29, 2006
  7. math(need 2nd opinion)

    1)Find a1 in a geometric series for which Sn=300,r=-3,and n=4 A)15 B)15/2 C)-15 D)1/15 I chose A 2)Find the sum of the infinite geometric series. Sigma sign with infinity symbol above and n=1 below. To the right 20(-1/4)n-1 A)25

    asked by Jon on December 12, 2007
  8. math

    1)Find a1 in a geometric series for which Sn=300,r=-3,and n=4 A)15 B)15/2 C)-15 D)1/15 I chose A 2)Find the sum of the infinite geometric series. Sigma sign with infinity symbol above and n=1 below. To the right 20(-1/4)n-1 A)25

    asked by Jon on December 12, 2007
  9. algebra

    1)Find a1 in a geometric series for which Sn=300,r=-3,and n=4 a.15 b.15/2 c.-15 d.1/15 answer=a 2)Find the sum of the infinite geometric series n=1 at the bottom of the sigma notation 20(-1/4)n-1 on the right side a.25 b.80/3 c.16

    asked by Marissa on August 23, 2007
  10. algebra

    1)Find a1 in a geometric series for which Sn=300,r=-3,and n=4 a.15 b.15/2 c.-15 d.1/15 answer=a 2)Find the sum of the infinite geometric series n=1 at the bottom of the sigma notation 20(-1/4)n-1 on the right side a.25 b.80/3 c.16

    asked by Marissa on August 26, 2007

More Similar Questions