Hitunglah n jika diketahui 1+2+4+8+…+2^(n-1) = 127

1+2+4+8…+2^(n-1) = 127
maka Sn=127, r=2, a =1

karna r>1
maka
Sn = a(r^(n-1) – 1) / r-1
127 = (2^(n-1) – 1) / 2-1
127 = (2^(n-1) – 1) / 1
127= 2^(n-1) – 1
128 = 2^(n-1)
2^7 = 2^(n-1)
maka
7= n-1
n=8