Infinite Geometric Series

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An infinite geometric series is a series of the form
       a + ar + ar² + ar³ + ar⁴ + ...

The sum of an infinite geometric series:
Sn= a + ar + ar² + ar³ + ar⁴ + ...
a + r (a + ar + ar² + ar³ + ar⁴ + ...)
a + rS

Solve the equation S= a + rS for S
S - rS = a
(1 - r)S = a
                a 
       S= 1 - r  ,  for -1 < r < 1.

if -1 < r < 1 for theses values of r, Sn has no limit or no sum.




Illustrative Examples:

Direction:  Determine if each infinite geometric series has a sum. If the sum exists, find the sum.

1.)     -5 + (-0.5) + (-0.05) + (-0.005) + ...

a= 5
r= 0.1
           a            -5             -5         
Sn= 1 - r  =  1 - 0.1 =     0.9    = -5.55 or 5.5


2.)     16 + 8 + 4 + 2 + ...

a= 16
r= ½
            a           16          16
Sn=  1 - r  =  1 - ½  =   ½   =  8


3.)       1 + ⅓ + 1/9 + 1/27 + ...

a= 1
r= 3
                    1        
Sn= 1 - r  =  1- 2  =  1    =  1



A/N: I'm back after death. Also, I already told you that I'm already grade 11. I took the HUMSS strand and I have a complete notes of one of our subject Earth and Life science. Should I transfer it here in wattpad? Just so I could help ':))

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