Question

Jika suatu barisan aritmatika suku ke-3 dan ke-5 = 10 dan 18, maka 15 suku pertama ??

Answer 1

Verified answer

Jawab
u3 = 10 
u5 = 18

u5 - u3  = 18 -10
(5-3) b = 8
2b = 8
b = 4

u3 = 10
a + 2b = 10
a + 8 = 10
a  = 2

Sn = n/2 (2a + (n-1)b))
s15 = 15/2 ( 4 + 14 (4))
s15 = 15/2 (60) = 450