deret geometri 1/8+1/4+1/2+....+16.Jumlah n suku pertama adalah?

deret geometri
1/8 + 1/4 + 1/2+......16
a = 1/8
r= 1/4 dibagi 1/8
  = 2

Un = ar^n-1
 16 = 1/8 x 2^n-1
16/1/8=2^n-1
128= 2^n-1
2^7 = 2^n-1
7 = n-1
7+1 =n
n = 8

Sn = a(r^n - 1)/r-1
s6 = 1/8(2^8-1)/2-1
     = 1/8(256-1)/1
     = 1/8 x 255
s6 = 255/8


maaf yah kalo salah....

Un = ar^n-1
16 = 1/8 x 2^n-1
16/1/8=2^n-1
128= 2^n-1
2^7 = 2^n-1
7 = n-1
n = 8

Sn = a(r^n - 1)/r-1
s8 = 1/8(2^8-1)/2-1
= 1/8(256-1)/1
= 1/8 x 255
s8 = 255/8