Question

Calcule o número de termos das seguintes P.G. (4, 8, 16,...,1024) R = 9 b) (9, 3, 1,...,1/81)

Answer 1

Boa tarde

PG 

termo geral
un = u1*q^(n - 1)

a)

(4, 8, 16,...,1024) 

q = 8/4 = 2

1024 = 4*2^(n - 1) 
2^(n - 1) = 1024/4 = 128
2^(n - 1) = 2^7

n = 8 termos

b)

(9, 3, 1,...,1/81)

q = 3/9 = 1/3

9*(1/3)^(n - 1) = 1/81 
(1/3)^(n - 1) = 1/729 = (1/3)^6

n = 7 termos