caranya no 7 bagaimana ya( rumus)

Mapel : Matematika
Bab : Barisan dan deret

a = 3,4,7,12,19
b = ..1..3...5...7
c = ...2....2...2

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

U12 = 3 + (12 - 1)1 + 1/2 (12 - 1)(12 - 2)2

U12 = 3 + 11 + 11 × 10

U12 = 14 + 110

U12 = 124

(A)

Mapel : Matematika
Materi : Barisan dan Deret
Kelas : 9

3, 4, 7, 12, 19 → a = 3
.. 1...3..5..7.... → b = 1
.... 2...2.2..... → c = 2

Rumus suku ke n

Un = 3 + (n - 1) + (n² - 3n + 2)
Un = 2 + n + n² - 3n + 2
Un = n² - 2n + 4

Maka, Suku ke 12 barisan

U12 = 12² - 2(12) + 4
U12 = 144 - 24 + 4
U12 = 144 - 20
U12 = 124