Question

Jumlah 15 suku pertama dari barisan 8, 11, 14, 17, 20, ...... adalah.....
tolong dibantu yah, terima kasih

Answer 1

Suku awal = a = 8
beda = b = 11-8 = 3

Sn = n/2 (2a + (n-1)b)
S15 = 15/2 [(2 x 8) + (15-1)3]
S15 = 7,5 [16 + (14 x 3)]
S15 = 7,5 (16 + 42)
S15 = 7,5 (58)
S15 = 435