Page 49 - DIGITAL BOOK MUHAMMAD AZWARDI NASUTION

Contoh 3:

Diketahui deret geometri dengan S = 4, S = 40
4
2
Tentukan rasio dan suku pertama

2
2
JAWAB (r − 1 )(r + ) 1
S 4 = 40 r − = 10
2

S 2 4 2 1

) 10
a (r 4 − ) 1 (r + 1 =

2
r − 1 = 10 r = 9

a (r 2 − ) 1 r =  3

r − 1 r = 3  a + a 3 = 4

a 4 = 4  a = 1

r = − 3  a − a 3 = 4

− a 2 = 4  a = − 2