jumlah 50 suku pertama deret -98, -95,-92,-89, ... adalah???

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

b = U2 - U1
b = (-95) - (-98)
b = -95 + 98
b = 3

Sn = n/2 . (2a + (n - 1) . b)
S50 = 50/2 . (2 . (-98) + 49 . 3)
S50 = 25 . (-196 + 147)
S50 = 25 . (-49)
S50 = -1.225