diketahui barisan bilangan 12,15,19,24,30,...,. nilai suku ke 12 barisan tersebut adalah

12, 15, 19, 24
3 4 5
1 1
2a = 1
a = 1/2
3a+b = 3
3.1/2+b = 3
b = 3/2
a+b+c = 12
1/2+3/2+c = 12
c = 10
Un = 1/2n2 + 3/2n + 10
U12 = 1/2.144 + 3/2.12 + 10
= 72 + 18 + 10
= 100