hitung jumlah 7 suku yang pertama dari DG :9+3+1+⅓+...

a = 9
r = 0,3
S7 = ???

S7 = 9(0,3^7 - 1)/0,3 - 1
S7 = 9(-0,9997813)/-0,7
S7 = -8,9980317/-0,7
S7 = 12,854331

9 + 3 + 1 + ⅓ + ...
a = 9
r = 3/9 = 1/3

Sn = a(1 - r^n)/(1 - r)
S7 = 9 (1 - (⅓)^7) / (1 - ⅓)
S7 = 9 (1 - 1/2187) / (2/3)
S7 = 9 (2186/2187) . 3/2
S7 = 9 . 3/2 . 2186/2187
S7 = 27/2 . 2186/2187
S7 = 1093/81
S7 = 13  40/81
S7 = 13, 494
S7 = 13,5