Tentukan banyak suku barisan geometri berikut! 1/6, 1/2, 3/2, ..., 81/2

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

r = U2 : U1
r = 1/2 : 1/6
r = 1/2 x 6/1
r = 3

Un = 81/2
a . r^(n - 1) = 81/2
1/6 . 3^(n - 1) = 81/2
3^(n - 1) = 81/2 . 6/1
3^(n - 1) = 243
3^(n - 1) = 3^5
n - 1 = 5
n = 5 + 1
n = 6

Banyak suku = 6

a = 1/6
r = 1/2 ÷ 1/6 = 3
Un = 1/6 3^n
81/2 = 1/6 3^n
3^n = 243 => 3^n = 3^5
n = 5
Sn = a(r^n - 1)
______
r - 1
S5 = 1/6 (3^5 - 1)
________
3 - 1
= 242
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