Question

a soma dos termos da PG: 2,6,18..., 486 é ?

Answer 1

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

a1=2
q=6/2
q=3

486=a1.q^(n-1)
486=2.3^(n-1)
3^(n-1)=486/2
3^(n-1)=243
3^(n-1)=3^5
n-1=5
n=5+1
n=6

S6=2.(3^6-1)/3-1
S6=2.(729-1)/2
S6=2.728/2
S6=728