Hitunglah jumlah deret aritmatika 1+4+7....u20

1 + 4 + 7 + ... + U20 => b = 4 - 1 = 3
U20 = a + 19b = 1 + 19(3) = 1 + 57 = 58

Sn = n/2 (a + Un) = 20/2 (1 + 58) = 10 (59) = 590

Materi Baret

Diketahui
a = 1
b = 3
n = 20
S20 = 20/2 (2×1 + 19 × 3) = 10 ( 2 + 57) = 10 × 59 = 590