Berapakah x dari 2+4+6+...+x = 930 ??

Bab Barisan dan Deret
Matematika SMP Kelas IX

a = 2
b = 4 - 2 = 2
Sn = 930

x = Un = ?

Sn = (n/2) x (2a + (n - 1) x b) = 930
(n/2) x (2 x 2 + (n - 1) x 2) - 930 = 0
n x (2 + n - 1) - 930 = 0
n x (n + 1) - 930 = 0
n² + n - 930 = 0
(n + 31) (n - 30) = 0
n + 31 = 0
n = - 31 (tidak memenuhi karena negatif)

n - 30 = 0
n = 30

Un = a + (n - 1) x b
U30 = 2 + (30 - 1) x 2
U30 = 2 + (29 x 2)
U30 = 2 + 58
U30 = 60

maka, x = 60