Question

Assinale o valor da soma dos 9 primeiros termos da PG (5,15,45..)

Answer 1

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

$q=\frac{15}{5}$

$q=3$

$S_9=\frac{a_1(q^9-1)}{q-1}$

$S_9=\frac{5(3^9-1)}{3-1}$

$S_9=\frac{5(19683-1)}{2}$

$S_9=\frac{5.19682}{2}$

$S_9=\frac{98410}{2}$

$S_9=49205$