Tentukan nilai Q jika 2+5+8+.....+Q = 1027

a = 2
 b = 5-2 =3
Sn = n/2 (2a +(n-1)b)
1027 = n/2 (4 + 3n - 3)
2054 = n( 3n + 1)
2054 = 3n^2 + n
3n^2 + n - 2054 = 0
(3n+79)(n-26) = 0
n = -79/3 atau n =26
Jadi n =  26
Q = Un = U26= a + 25b = 2 + 75 = 77