Dari suatu barisan aritmatika di ketahui U4 = 8 U8 = 16 . Suku ke 12 adalah

U12 = 2x12 = 24. mohon maaf kalo salah

U4 = a + (4-1) b = 8
= a + 3b = 8

U8 = a + (8-1) b = 16
= a + 7b = 16

A + 3b = 8
A + 7b = 16 -
———————
= -4b = -8
B = -8/-4 = 2

A + 3b = 8
A + 3.2 = 8
A + 6 = 8
A = 8-6 = 2

Maka,

U12 = a + (12-1) b
= 2 + 11b
= 2 + 11. 2
= 2 + 22
= 24

Jadi U12 = 24

Semoga membantu :)