jumlah delapan suku pertama dari deret [tex](2 + x) + 5x + (14 + x) + ...[/tex] adalah...

u1 = a = (2+x)
u2 = a+b = 5x
u3 = a+2b = (14+x)

a+b = 5x
2+x+b = 5x
b = 4x -2....(1)

a+2b = 14+x
2+x +2b = 14+x
b = 6 (masuk ke pers 1)

6 = 4x-2
x = 2

Deret aritmatika :
4,10,16,22... dst..
a = 4
b = 6

S8 = (n/2)(2a + (n-1)b)
S8 = (8/2)(2.4+(8-1)6)
S8 = 4(8+42)
S8 = 200