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n = 6
a = U1 = 2
U6 = 486

Un = ar^(n-1)
U6 = 486
ar⁵ = 486
2 x r⁵ = 486
r⁵ = 486/2
r⁵ = 243
r = 3

Panjang tali mula mula
S6 = a (r⁶ - 1) / (r - 1)
S6 = 2 (3⁶ - 1) / (3 - 1)
S6 = 2 (729 - 1) / 2
S6 = 2 (728) / 2
S6 = 728 m

Jadi, panjang tali mula mula adalah 728 m

diketahui:
n = 6
U1 = 2
U6 = 486

ditanya:
S6

dijawab:
U6 = a.r^5 = 486
U1 = a......... = 2
r^5 = 486÷2
r^5 = 243
r = 3

Sn = a(r^n-1) / r-1
S6 = 2(3^6-1 / 3-1
S6 = 2(728) / 2
S6 = 1456/2
S6 = 728 (B)