hasil dari 9+27+81+.....+2187

9+27+81+.....+2187 = ....
a = 9
r = 27/9
r = 3
Un = arⁿ-¹
2187 = 9 x 3ⁿ-¹
3ⁿ-¹ = 2187/9 = 243
3ⁿ-¹ = 3^5
n = 5+1
n = 6

S6 = 9 x (3^6 -1)/(3-1) = 9/2 x (729-1)
= 9 x 728/2
= 9 x 364
= (10-1) x 364
= 3.640 - 364
= 3.276