Question

Dada a PG (2,6,18,...,39366),determine o numero de termos.

Answer 1

Dados:

$q= \frac{a_2}{a_1}\\ \\q=3$

$a_1=2\\ \\a_n=39366\\ \\n=?$

Termo geral:

$a_n=a_1*q^{n-1}\\ \\39366=2*3^{n-1}\\ \\19683=3^{n-1}\\ \\\not3^{9}=\not3^{n-1}\\ \\n-1=9\\ \\\boxed{\therefore~n=10}$