jumlah 8 suku pertama deret aritmatika berikut ini 2+x , 5x , x+14 adalah

U1 = 2 + x
U2 = 5x
U3 = x + 14

2.U2 = U1 + U3
2(5x) = 2 + x + x + 14
10x = 2x + 16
10x - 2x = 16
8x = 16
x = 16/8
x = 2
U1 = 2 + x = 2 + 2 = 4
U2 = 5(2) = 10
b = U2 - U1 = 10 - 4 = 6
Sn = n/2 (2.U1 + (n-1)b)
S8 = 8/2 (2(4) + (8-1)6)
= 4(8 + 42)
= 4(50)
= 200