Question

Deret geometri bantu aku kk :D

Answer 1

# deret geometri

no. 1
U₁ = a = 1 dan rasio r = U₂/U₁ = 2/1 = 2

Sn = a.[rⁿ - 1] / [r - 1]
S₁₂ = 1.[2¹² - 1] / [2 - 1]
S₁₂ = [2⁶ + 1][2⁶ - 1]
S₁₂ = 65 x 64 = 4160

no.2
U₁ = a = 1  dan rasio r = U₂/U₁ = [1/3] / 1 = 1/3

Sn = a.[1 - rⁿ] / [1 - r]
S₆ = 1.[1 - (1/3)⁶][1 - 1/3]
S₆ = 3/2.[1 + (1/3)³][1 - (1/3)³]
S₆ = 3/2.[1 + 1/27][1 - 1/27]
S₆ = 3/2.[28/27][26/27]
S₆ = 364/243

no.3
U₁ = a = 1 dan rasio r = U₂/U₁ = -3/1 = -3

Sn = a.[rⁿ - 1] / [r - 1]
S₈ = 1.[(- 3)⁸ - 1] / [(- 3) - 1]
S₈ = [3⁴ + 1][3⁴ - 1] / - 4
S₈ = [82 x 80] / -4
S₈ = - 1640