bantu jawab ya... tolong

Suku pertama
U₁ = 2²⁻ⁿ
U₁ = 2²⁻¹
U₁ = 2¹
U₁ = 2

Suku kedua
U₂ = 2²⁻²
U₂ = 2⁰
U₂ = 1

Rasio
r = U₂/U₁
r = 1/2

Jumlah tak hingga
S∞ = a/(1-r)
S∞ = U₁/(1-r)
S∞ = 2/(1-1/2)
S∞ = 2/(1/2)
S∞ = 2 : 1/2
S∞ = 2 × 2/1
S∞ = 4/1
S∞ = 4