Suatu deret geometri u1 = 2 u4 = 2/27 jumlah 5 suku pertamanya adalah

a.r³ = 2/27
2.r³ = 2/27
r³ = 2/27×2
r³ = 1/27
r = 1/3

S5 = a.(1-rⁿ)÷(1-r)
S5 = 2.(1-(1/3)^5)÷(1-1/3)
S5 = 2(1-1/243) ÷ 2/3
S5 = 2(242/243)÷ 2/3
S5 = 484/243 × 3/2
S5 = 726/243