U2=16, U6=1296. Tentukan jumlah 8 suku pertama deret geometri

r = akar^4 (1296/16) = akar^4 (81) = 3
U2 = a.r
6 = a.3
a = 2

Sn = a(r^n - 1)/(r-1)
S8 = 2(3^8 - 1)/(3-1)
= 3^8 - 1
= 6561 - 1
= 6560