Question

PG ( 2; 3 ; 4,5) - escreva o termo geral da PG. Calcule a9 e s9.

Answer 1

Bom dia Fernanda

PG

u1 = 2
u2 = 3
u3 = 4.5

razão
q = u2/u1 = 3/2

o termo geral 
un = u1*(n - 1)
un = 2*(3/2)^(n - 1)

u9 = 2*(3/2)^8 
u9 = 6561/128
soma
Sn = u1*(q^n - 1)/(q - 1)

S9 = 2*( (3/2)^9 - 1)/(3/2 - 1)
S9 = 4*(  (3/2)^9 - 1)
S9 = 4*( 19683/512 - 512/512)
S9 = 4*(19171/512)
S9 = 19171/128