Question

Calcule a soma dos termos da PG (5,15, 45,..., 3645).

URGENTE!

Answer 1

Resposta:

a1=15

a2=15

q=a2/a1=15/5=3

an=a1*q^(n-1)

3645=5*3^(n-1)

3645/5=3^(n-1)

729=3^(n-1)

3^5=3^(n-1)

5=n-1  ==>n=6

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

Sn=5*(1-3^6)/(1-3)

Sn =(5/2)* (3^6-1)

Sn=1820