suku pertama dan kelima suatu barisan geometri berturut-turut 5 dan 80. Suku ke-9 barisan tersebut adalah... TOLONG CARANYA

U1 = a = 5
U5 = ar^4 = 80

U5 / U1 = ar^4 / a = 80 /5
r^4 = 16
r = 2

Un = ar^(n-1)
U9 = ar^8
= 5 . 2^8
= 5 . 256
= 1.280

Langsung aja y

r = (U5 : U1)^1/(5-1)
r = (80 : 5)^¼
r = 16^¼
r = 2

U9 = U5 × r⁴
U9 = 80 × 2⁴
U9 = 80 × 16
U9 = 1.280

Semoga berguna +_+