suku ke-9 barisan 162,54,18,6,2,.... adalah... a.2/9 b.2/27 c.2/81 d.2/243

a = 162
r = ?

Kita cari dulu r

U2 = 162×r^2-1
54 = 162×r1
54 = 162r
r = 54 / 162
r =1/3

U9 = ar^9-1
U9 = 162 × 1/3^8
U9 = 162 × 1/6561
U9 = 162/6561

Barisan geometri
Dik. a = 162
r = 54/162 = 1/3
Dit. U9 =...?
Jawab :
U9 = ar^n-1
U9 = 162 . 1/3^8
U9 = 162 . 1/6,561
U9 = 2/81 (C)