# Algebra

1. Why cant you use the formula of the infinite geometric series on 1/81 + 1/27 + 1/9 + 1/3 + .....

2. Using concepts of infinite geometric series, show that 0.9999 ..... = 1.

1. 👍 0
2. 👎 0
3. 👁 148
1. r = (1/27) ÷ (1/81)
= 3
so the series diverges, that is, the terms are getting larger.
Clearly the sum will get larger and larger and eventually become infinitely large.

That is why for the formula
Sum (infinite number of terms) = a/(1-r)
part of the definition will be |r| < 1

2.
let .99999.. = .9 + .09 + .009 + ....
so a = .9 , and r = .1
sum(all terms) = .9/(1-.1)
= .9/.9
= 1

1. 👍 0
2. 👎 0
posted by Reiny

## Similar Questions

1. ### algebra

Can someone please help me with this problem? Thanks! Evaluate the infinite geometric series: 8+4+2+1+... I thought you needed to know the number of terms to evaluate, but how do you know them if it is infinite? The limit of Sn =

asked by Mercy on May 30, 2007
2. ### 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
3. ### 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 24, 2007
4. ### algebra(check)

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 24, 2007
5. ### 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
6. ### 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
7. ### Algebra 2

Describe an infinite geometric series with a beginning value of 2 that converges to 10. What are the first four terms of the sequence? a{1} = first term of series ∞ Infinite Sum = ∑ a{1} • r^(n – 1) = a{1} ⁄ (1 – r)

asked by Ke\$ha on March 31, 2016
8. ### 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
9. ### algebra

Okay, I was taught that if a geometric series is infinite and it diverges then it has no limit and no sum. Looking back in my notes, I found an example of finding the value for a divergent series? Is this possible? The sum of an

asked by Jane E. on May 31, 2007
10. ### 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

More Similar Questions