Question

calcule a soma dos oito termos da P,G (-5,10,20..)

Answer 1

P.G(-5,10,20,....)
A 1 = -5
A 2 = 10
q = a 2/a 1
q = 10/-5
q = -2
Sn = a 1 .q^n - 1)/q - 1
S8 = -5 . (-2^8 - 1 )/-2 - 1
S 8 = -5 . (256 - 1 ) / -3
S8 = -5(255)/-3
S8 = -1275/-3
S8 = +425