diketahui barisan arirmatikadengan u7=32 dan U12=47. suku ke-30 barisan tersebut adalah

U7 = 32
a+6b = 32 .... (1)

U12 = 47
a+11b = 47 .... (2)

eliminasikan
a+6b = 32
a+11b = 47
---------------- -
-5b = -15
b = 3

a+6b = 32
a+18 = 32
a = 14

U30 = a + (29)b
= 14 + (29)3
= 101

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

b = (U12 - U7)/(12 - 7)
b = (47 - 32)/5
b = 15/5
b = 3

U30 = U12 + 18b
U30 = 47 + 18 . 3
U30 = 47 + 54
U30 = 101