Jawabanmu

2014-03-27T22:54:40+07:00
U2 = a.r = 81
U5 = a.r^4 = 3
keduanya di eliminasi, jadi, r^3 = 3/81
r^3 = 1/27
r = 1/3 , karena r udah ketemu, nyari a , yaitu a. r = 81, a = 81.3 = 243
trus masukin rumus Sn
S8 = a (1 - r^n) / 1 - r
S8 = 243 (1 - (1/3)^8 / 1- (1/3)
S8 = 243 . 6560 .3 /6561.2
S8 = 364 4/9 (C)
2014-03-28T02:22:01+07:00
Ar^4/ar = 3/81
r^3 = 1/27
r = ∛(1/27)
r = 1/3

a = 81 x 3 = 243
8 suku pertama = 243,81,27,9,3,1,1/3,1/9,
total = 364 4/9