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Verified answer
Mapel: MatematikaBab: Barisan dan Deret
Diketahui:
Barisan Geometri
U1 = 81
U5 = 1
Ditanyakan:
S8?
Jawab:
U1 = 81
a = 81
U5 = 1
ar^4 = 1
81.r^4 = 1
r^4 = 1/81
r^4 = (1/3)^4
r = 1/3
Sn = (a (1 - r^n)) / (1 - r)
S8 = (81 (1 - (1/3)^8)) / (1 - 1/3)
= (81 (1 - 1/6561)) / (2/3)
= (81 (6560/6561) (3/2)
= 121,48