Question

Hitunglah jumlah deret aritmtika yang suku pertamanya= 10, suku terakhir= 130, dan U 9 - U 6= 60!

Answer 1

U9 - U6 = 60
(a + 8b) - (a + 5b) = 60
a+ 8b -a -5b = 60
3b = 60
b = 20

Un = a + (n-1)b
130 = 10 + (n-1) 20
130 =  10 + 20n -20
130 - 20 -10 = 20n
100 = 20n
n = 100/2
n = 50

Sn = 1/2n (a + Un)
Sn = 1/2(50) (10 + 130)
Sn = 25 (140)
Sn = 3.500