tentukan hasil dari 2+4+8+...+128=

a = 2
ar = 4
2r = 4
r = 2

Un = arⁿ⁻¹
128 = 2. 2ⁿ⁻¹
2ⁿ⁻¹ = 128 / 2
2ⁿ⁻¹ = 64
2ⁿ⁻¹ = 2⁶
n - 1 = 6
n = 7

Sn = [a(1-rⁿ)] / 1 - r
S7 = [2(1-2⁷)] / 1 - 2
S7 = [2 (1 - 128)] / (-1)
S7 = - (2 x (-127))
S7 = 254