Question

a soma dos oito primeiros termos da pg (16,8,4...) é?

Answer 1

P.G.(16,8,4,.....)
q = a 2/a 1
q = 8/16
q = 1/2
a n = a 1 . q^n - 1
a 8 = 16 . (1/2)^8 - 1
a 8 = 16 . (1/2)^7
a 8 = 16 . 1/128
a 8 = 16/128
a 8 = 1/8

S 8 = a n . q - a 1 /q - 1
S 8 = 1/8 . 1/2 - 16 / 1/2 - 1
S 8 = 1/16 - 16 / -1/2
S 8 = (1 - 256) /16   /  -1/2
S 8 = -255/16  / - 1/2
S 8 = -255/16 x -2/1
S 8 = +510/16 simplifica por 2
S 8 = 255/8
Resposta letra c)