suku ke-22 dari barisan bilangan 12,20,30,42,56,...adalah... a. 624 b.600 c. 575 d.552

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

12, 20, 30, 42, 56, ... → a = 12
....8....10....12....14...... → b = 8
.......2......2.....2.... → c = 2
n = 22

Un = a + (n - 1) . b + 1/2 . (n - 1) . (n - 2) . c
U22 = 12 + 21 . 8 + 1/2 . 21 . 20 . 2
U22 = 12 + 168 + 420
U22 = 600