Tentukan jumlah deret aritmetika berikut B. 222+214+206+198..+30

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

b = U2 - U1
b = 214 - 222
b = -8

Un = 30
a + (n - 1) . b = 30
222 + (n - 1) . (-8) = 30
(n - 1) . (-8) = 30 - 222
n - 1 = -192/(-8)
n = 24 + 1
n = 25

Sn = n/2 . (a + Un)
S25 = 25/2 . (222 + 30)
S25 = 12,5 . 252
S25 = 3.150