4,8,14,22 cari rumus suku ke -n

Bab Barisan dan Deret
Matematika SMP Kelas IX

4, 8, 14, 22, ... → a = 4
..4...6...8.... → b = 4
.....2...2.... → c = 2

Un = a + (n - 1) b + 1/2 x (n - 1) x (n - 2) x c
Un = 4 + (n - 1) x 4 + 1/2 x (n² - 3n + 2) x 2
Un = 4 + 4n - 4 + n² - 3n + 2
Un = n² + n + 2