Diketahui barisan bilangan 12,20,30,42,56..... suku ke-22 adalah....

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