Diketahui suatu barisan aritmatika dengan U5=7 dan U8=13. Suku ke-20 adalah...

U5 = a + 4b = 7
U8 = a + 7b = 13
______________-
- 3b = 6
b = 2

a + 4b = 7
a + 4(2) = 7
a + 8 = 7
a = 7 - 8
a = - 1

U20 = a + 19b
= (- 1) + 19(2)
= - 1 + 38
= 37

Jgn lupa tekan tombol "Thank You" ya :)

U5 = 7
U8 = 13

Jadi ditambah 2, setiap mau Naik U
U5 = 7
U6 = 9
U7 = 11
U8 = 13
U9 = 15
U10 = 17
U11 = 19
U12 = 21
U13 = 23
U14 = 25
U15 = 27
U16 = 29
U17 = 31
U18 = 33
U19 = 35
U20 = 37

Jadi U20 = 37