Question

Qual a soma dos 10 primeiros termos da PG (-10,20.-40,80,...)? *

Answer 1

Resposta:

3410

Explicação passo-a-passo:

$q=\frac{20}{-10} \\\\q=-2\\\\\\S_n=a_1*(\frac{q^n-1}{q-1})\\\\S_1_0=-10*(\frac{(-2)^1^0-1}{-2-1})\\\\S_1_0=10*(\frac{2^1^0-1}{3})\\\\S_1_0=10*(\frac{1024-1}{3})\\\\S_1_0=10*(\frac{1023}{3})\\\\S_1_0=10*341\\\\S_1_0=3410$