Suku ke -20 dari barisan bilangan 5, 10, 17, 26, 37,... adalah... a. 442 b.642 c. 842 d.862

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

5, 10, 17, 26, 37, ... → a = 5
...5,...7,...9,...11,.... → b = 5
.......2...2....2..... → c = 2
n = 20

Un = a + (n - 1) . b + 1/2 . (n - 1) . (n - 2) . c
U20 = 5 + 19 . 5 + 1/2 . 19 . 18 . 2
U20 = 5 + 95 + 342
U20 = 442

5 a = 5
b = 5
c = 2

Un = a+(n-1) × b + 1/2 × (n-1) × (n-2) × c

U₂₀ = 5+(20-1) × 5 + 1/2 × (20-1) × (20-2) × 2

U₂₀ = 5 + 19 × 5 + 1/2 × 19 × 18 × 2

U₂₀ = 5 + 95 + 19 × 18

U₂₀ = 5 + 95 + 342

U₂₀ = 442 [ opsi. A ]