Diketahui barisan bilangan 3 4 7 12 19 ... nilai suku ke-12 berdasarkan pola barisan tersebut adalah

Cara manual : 3,4,7,12,19,28,39,52,67,84,103,124
Jadi suku ke 12 = 124

→ 2a = 3
a = 3/2
→ 3a+b = 1
3(3/2)+b = 1
b = 1 - 9/2
b = -7/2
→ a+b+c = 2
3/2 - 7/2 + c = 2
c = 2 + 4/2
c = 4
→ Un = an² + bn + c
U12 = 3/2×12² - 7/2×12 + 4
= 3/2×144 - 7×6 + 4
= 3×72 - 42 + 4
= 216 - 42 + 4
= 174 + 4
= 178

Semoga membantu^^