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Verified answer
Barisan Geometri2, 8, 32, ...
a = 2
r = U2/U1 = 8/2 = 4
a. Rumus suku ke n (Un)
Un = ar^(n - 1)
Un = 2 . 4^(n - 1)
Un = 2 . 2^2(n - 1)
Un = 2^(2n - 2 + 1)
Un = 2^(2n - 1)
b.
Un = 2048
2^(2n - 1) = 2048
2^(2n - 1) = 2^11
2n - 1 = 11
2n = 11 + 1
n = 6
2048 adalah suku ke 6
U6 = 2048
c. Jumlah 7 suku pertama (S7)
Sn = a(r^n - 1)/(r - 1)
S7 = 2(4^7 - 1)/(4 - 1)
S7 = 2 × 16383/3
S7 = 10922