Question

Suku dari ke-40, barisan bilangan.... 12,20,30,42 adalah....

Answer 1

Verified answer

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

U1 = 12 = 3 . 4
U2 = 20 = 4 . 5
U3 = 30 = 5 . 6
U4 =42 = 6 . 7
.
.
Un = (n + 2) . (n + 3)

U40 = (40 + 2) . (40 + 3)
U40 = 42 . 43
U40 = 1.806

Answer 2

Verified answer

12  20  30  42
    8   10   12
       2     2

a = 12
b = 8
c = 2

Un = a + b(n - 1) + c(n - 1)(n - 2)/ 2
Un = 12 + 8n - 8 + 2(n² - 3n + 2)/2
Un= n² + 5n + 6

U40 = 40² + 5(40) + 6
U40 = 1600 + 200 + 6
U40 = 1806