Question

Quantos termos devemos considerar na PG (3,6,...) para obter soma igual a 765?

Answer 1

a1 = 3
a2 =6
q=a2/a1
q=6/3
q=2
Sn= 765
n=...
Sn=a1.(1-q^(n-1)) / 1-q
765/3= 3.(1-2^(n-1)/ (-1)
(1-2^(n-1)=-255
-2^(n-1) = -256
-2^(n-1)=2^7
n-1=7
n=7+1
n= 8