Suku ke 40 dari 3,5,9,15,23, ...... Adalah? (Tolong ya pakai cara)

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

3, 5, 9, 15, 23, ... → a = 3
..2...4...6...8..... → b = 2
....2....2...2... → c = 2
n = 40

Un = a + (n - 1) . b + 1/2 . (n - 1) . (n - b) . c
U40 = 3 + 39 . 2 + 1/2 . 39 . 38 . 2
U40 = 3 + 78 + 1.482
U40 = 1.563