Question

Determinar o número de termos da P.G. (-1,-2,-4,...,-512). Calcule a soma dos primeiros termos

Answer 1

q ⁿ-¹ = an/a1
2ⁿ-¹ = -512/-1
2ⁿ-¹ = 512
2ⁿ-1 = 2^9
n-1 = 9
n = 10 termos ✓

sn= a1.(qⁿ -1) / q-1
sn= -1.(2ⁿ -1) / 2-1
sn= -2ⁿ +1 / 1
sn= 1 -2ⁿ ✓