a. 2 + 6 + 18 + 54 +……:S10
b. 1 – 3 + 9 – 27 + 81 -……:S15
Tentukan jumlah deret geometri di bawah ini
nomor a
a = 2
r = U2 / a
r = 6/2
r = 3
Sn = a (rⁿ – 1) / (r-1)
S10 = 2 (3¹⁰ – 1) / (3-1)
S10 = 59048 ✔️
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nomor b
a = 1
r = -3 /1
r = -3
Sn = a (1 – rⁿ) / (1 – r)
S15 = 1 [ 1 – (-3)¹⁵ ] / (1+3)
S15 = 3.587.227 ✔️
______
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