Jawabanmu

2014-06-16T07:04:36+07:00
Sn= 2 (3^n+1 - 3)
S1= 2 (3^1+1 - 3)
S1= 2 (3^2 - 3)
S1= 2 (9-3)= 2 . 6
S1 = 12 = a

Sn= 2 (3^n+1 - 3)
S2= 2 (3^2+1 - 3)
S2= 2 (3^3 - 3)
S2= 2 (27-3)= 2 . 24
S2 = 48 = a + a.r 

a + a . r = 48
12 + 12 . r = 48
12. r = 36
r = 3

a+r =12+3 = 15    C. jawabannya
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