Question

determine a soma da pg (2,-4,8,-16,32,-64,128)

Answer 1

Oi Samilla

PG

u1 = 2
u2 = -4

q = u2/u1 = -4/2 = -2

termo geral
un = u1*q^(n - 1)

2*(-2)^(n - 1) = 128
(-2)^(n - 1) = 64 = 2^8 

n - 1 = 8
n = 9 termos

soma
Sn = u1*(q^n - 1)/(q - 1)

S9 = 2*((-2)^9 - 1)/(-2 - 1)
S9 = 2*(-512 - 1)/(-3)
S9 = 2*513/3 = 1026/3

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