Diketahui suku ke 3 dan suku ke 8 barisan aritmetika masing-masing 13 dan 38 suku ke 6 barisan aritmetika tersebut

U3 = a + 2b = 13
U8 = a + 7b = 38
_____________ -
-5b = -25
b = 5

a+2b = 13
a+2(5) = 13
a + 10 = 13
a = 13-10
a = 3

U6 = a+5b = 3+5(5) = 3+25 = 28

Barisan Aritmatika

U8 = a + 7b = 38
U3 = a + 2b = 13

Eliminasi
U8 – U3

a + 7b = 38
a + 2b = 13
__________ _
5b = 25
b = 25/5
b = 5

Substitusi
a + 2b = 13
a + (2×5) = 13
a + 10 = 13
a = 13 – 10
a = 3

U6 ?

U6 = a + 5b
U6 = 3 + (5×5)
U6 = 3 + 25
U6 = 28