Question

Considera a P.G.(1,-2,4,-8,...)calcule a soma de seus doze primeiros termos ?

Answer 1

P.G.(1,-2,4,-8,...)
q = a 2 / a 1
q = -2/1
q = -2
A 12 = a 1 . q^n - 1
a 12 =  1 . (-2)12 - 1
a 12 = 1. (-2)^11
a 12 = 1. (-2048)
a 12 = -2048 

S 12 = A 1 / 1 - q
S 12 = 1/ 1 - (-2)
S 12 = 1 / 1 + 2
S 12 = 1/ 3