Question

Dari barisan aritmatika diket U9 = 63 dan U16 = 105. Jumlah 20 suku pertama adalah

Answer 1

Verified answer

Kelas 9 Matematika
Bab Barisan dan Deret Bilangan

b = (U16 - U9)/(16 - 9)
b = (105 - 63)/7
b = 42/7
b = 6

a = U9 - 8b
a = 63 - 8 . 6
a = 63 - 48
a = 15

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

S20 = (20/2) . (2 . 15 + 19 . 6)
S20 = 10 . (30 + 114)
S20 = 10 . 144
S20 = 1.440