Page 70 - DIGITAL BOOK MUHAMMAD AZWARDI NASUTION

EXAMPLE 2

Given that geometric series with S = 4, S = 40
2
4

S 4 = 40

S 2 4

a (r 4 − ) 1

r − 1 = 10

a (r 2 − ) 1

r − 1

r 4 − 1 = 10

r 2 − 1 r + 1= 10
2

(r − 1 )(r + ) 1 = 10 2
2
2

r − 1 r = 9  r =  3
2

r = 3