Suatu barisan Aritmatika jika U3=13 dan U11=45 maka U21=...... Tolong bantu yaaa... Beserta caranya....

Matematika

b = (U11 - U3) / (11 - 3)
b = (45 - 13) / 8
b = 32/8
b = 4

U21 = U11 + 10b
U21 = 45 + 10(4)
U21 = 45 + 40
U21 = 85

Kelas 9 Matematika
Bab 6 - Barisan dan Deret Bilangan

Aritmatika
Un = a + (n - 1)b

U3 = a + 2b = 13
U11 = a + 10b = 45

Eliminasi nilai a
a + 2b = 13
a + 10b = 45
__________ _
-8b = -32
b = -32/-8
b = 4

Substitusikan nilai b

a + 2b = 13
a + 2(4) = 13
a + 8 = 13
a = 13 - 8
a = 5

U21 = a + 20b
U21 = 5 + 20(4)
U21 = 5 + 80
U21 = 85