Jawabanmu

2014-02-02T11:16:59+07:00
A = 128
r = -64/128 = -1/2

un= ar^n-1
un = 128 . (-1/2)^n-1
un = 128 . ((-2)^-1)^n-1
un = 128 . -2^1-n

-1 = 128 . -2^1-n
-1/128 = -2^1-n
-2^-7= -2^1-n
-7 = 1-n
n= 8