diketahui barisan aritmatika U4=14 U7=23 maka U15=

Diketahui
U₄ = a + 3b = 14 ................(1)
U₇ = a + 6b = 23 ................(2)
maka
a + 3b = 14
a + 6b = 23  - 
-------------------
      3b = 9
        b = 3
Subtitusikan nilai b = 3 ke pers. a + 3b = 14
a + 3b = 14
a + 3(3) = 14
a + 9 = 14
a = 14 - 9
a = 5

jadi 
U₁₅ = a + 14b
U₁₅ = 5 + 14(3)
U₁₅ = 5 + 42
U₁₅ = 47

Dik:
U4 = 14
U7 = 23

Dit:
U15 = ?

Jawab:
U4 = a + (4-1) b
U7 = a + (7-1) b

23 = a + 6b
14 = a + 3b
__________-
9 = 3b
b = 3
U4 = a + 3b
14 = a + 9
a = 5

U15 = a + (n-1) b
U15 = 5 + (14) 3
U15 = 42 + 5
U15 = 47