Question

Quantos termos tem a PG (243,81,27.....1/3^10)?

Answer 1

Boa noite AnnaLuiza

PG

u1 = 243
u2 = 81

q = u2/u1 = 81/243 = 1/3 

un = (1/3)^10 

termo geral

un = u1*q^(n - 1) 

(1/3)^10 = 243 * (1/3)^(n - 1)

(1/3)^10 = 3^5 * (1/3)^(n - 1)

3^-10 = 3^5 * 3^(1 - n)

3^(1 - n) = 3^-10/3^5 = 3^-15 

1 - n = -15 
n - 1 = 15 

n = 16 termos