Question

Calcule a soma dos 5 primeiros termos da PG onde a5=162 e q=3
$a5=162 e q=3$

Answer 1

$a5=a1.q^{4} \\162=a1 (3^{4}) \\162=a1 (81)\\ \frac{162}{81} =a1\\\\a1=2$

$S_n = a_1 \frac{1-q ^{n}}{1-q} \\\\S_5 = 2 \frac{1-3 ^{5}}{1-3} \\\\S_5 = 2 \frac{-242}{-2} \\\\S_5 = 242$