16. Dari Barisan Aritmetika Diketahui U3=18 dan U7 =38. Dan Jumlah 24 suku pertama adalah? Dengan Contohnya

U3 = a + 2b = 18
U7 = a + 6b = 38

U7 - U3 = 20
4b = 20
b = 5

a + 2b = 18
a + 10 = 18
a = 8

Sn = n/2 (2a + (n-1)b)
S24 = 24/2 (2.8 + 23.5)
S24 = 12 (16 + 115)
S24 = 12 × 131
S24 = 1572

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

b = (U7 - U3)/(7 - 3)
b = (38 - 18)/4
b = 20/4
b = 5

a = U3 - 2b
a = 18 - 2 . 5
a = 18 - 10
a = 8

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

S24 = 24/2 . (2 . 8 + 23 . 5)
S24 = 12 . (16 + 115)
S24 = 12 . 131
S24 = 1.572