Question

Calcule a soma dos 8 termos da PG abaixo: {, 2, 6, 18, 54, ...}

Answer 1

s = a1.(q^n - 1) / q-1

s = 2.(3⁸ - 1) / 3-1

s = (3⁸ - 1)

s = 6560

Answer 2

$\sf S_{n} = \dfrac{a_{1}\cdot (q ^{n} - 1)}{q - 1}$

$\sf S_{8} = \dfrac{2\cdot (3 ^{8} - 1)}{3 - 1}$

$\sf S_{8} = \dfrac{2\cdot (6.561- 1)}{2}$

$\sf S_{8} = \dfrac{2\cdot 6.560}{2}$

$\sf S_{8} = \dfrac{13.120}{2}$

$\red{\sf S_{8} = 6.560}$