1.Tentukan banyaknya suku untuk setiap barisan geometris berikut a.5,10,20,...,1280 b.-128,64,-32,...,1/16

a.
a= 5
r= 2
Un = 1280
ar^n-1 = 1280
5 (2^ n-1) = 1280
(2^ n-1 )= 256
2^n-1 = 2^8
n-1 = 8
n = 9

b.
a= -128
r = -1/2
Un = 1/16
ar^n-1 = 1/16
-128 (-1/2)^n-1 = 1/16
(-1/2)^n-1 = 1/16 : -128
(-1/2 )^n-1 = -1/2048
(-1/2 )^n-1 = -1/2 ^ 11
n-1 = 11
n = 12