tolong dibantu yah teman2...........

Sn = a(1 - r^n) /1-r
r = U2 / U1 = 2/1 = 2

S8 = 1(1-2^8) / 1-2
=> 1-256/-1
=> -255 /-1
=> 255

berikut caranya semoga membantu