no 3, caranya sekalian

Bab Pola Bilangan

U4 = ar^(4 - 1)
ar^3 = 8

U5 = ar^(5 - 1)
ar^4 = 4


ar^3 × r = U5
8 × r = 4
r = 4/8
r = 1/2

ar^3 = 8
a(1/2)^3 = 8
a(1/8) = 8
a = 8 × 8 = 64

Sn = a(1 - r^n)/(1 - r)
S5 = 64(1 - (1/2)^5)/(1 - 1/2)
S5 = 64(1 - 1/32)/ 1/2
S5 = 64 × 31/32 × 2
S5 = 124 lembar

Banyak uang
= 124 × 2.000
= Rp248.000,00

nggak tau aku caranya