Jumlah aritmatika 2+9+16+...…..sampai 20 suku????

Bab Barisan dan Deret
Matematika SMP Kelas VIII

b = U2 - U1
b = 9 - 2
b = 7

Sn = (n/2) . (2a + (n - 1) . b)

S20 = (20/2) . (2 . 2 + 19 . 7)
S20 = 10 . (4 + 133)
S20 = 10 . 147
S20 = 1.470