Suku ke 70 barisan bilangan 8,15 ,24,35 adalah

(i) : 8, 15, 24, 35
(ii) : 7, 9, 11 (selisih pertama)
(iii): 2,2 (selisih ke 2)

(iii) : 2a = 2
a = 1
(ii) : 3a + b = 7
3×1+ b = 7
b = 7-3
b = 4
(i) : a + b + c = 8
1 + 4 + c = 8
5 + c = 8
c = 8 - 5
c = 3
Un = an^2 + bn + c
= 1×70^2 + 4×70 + 3
= 4900+ 280 +3
= 5183