Suatu barisan geometri : 16, 8, 4, 2, maka jumlah n suku pertama adalah

a = 16
r = 8/16 = 1/2

[tex]sn = \frac{16(1 - ( \frac{1}{2})^{n}) }{1 - ( \frac{1}{2}) } [/tex]
semoga membantu :)

un=ar^n-1
un=16×(1/2)^n-1
un=2⁴×(1/2)^n-1
un=2⁴/2^n-1
un=2^4-n+1
un=2^5-n

sn=a(r^n-1)/r-1
sn=16(1/2^n-1)/1/2-2/2
sn=2⁴(1/2^n -1)/-1/2
sn=2^5-n+1 -2⁴/-1
sn=-(2^6-n)+2⁴