Question

Determine a soma dos 20 primeiros termos da PG(1,3,9,27)

Answer 1

PG (1,3,9,27)

$Sn=a1 *(q^n-1) /q-1$

a1=1
q= 3/1= 3

S20=1*(3^20 -1)/3-1= (3486784401-1)/2=1743392200