An=3n an≤100 Найти Sn

Question

An=3n an≤100 Найти Sn

Answer 1

3n ≤ 100
n ≤ 100:3
n ≤ 33,(3)

n = 33
a1 = 3
a33 = 99

S33 = (a1 + a33)*33/2 = (3 + 99)*33/2 = 102*33/2 = 51*33 = 1683