Suku ke-3 dan ke-9 suatu barisan aritmetika adalah 17 dan 47. Suku ke-27 barisan tersebut adalah ....

U3 = a + (3-1) b = 17
U3 = a + 2b = 17

U9 = a + (9-1) b = 47
U9 = a + 8b = 47

pakai rumus eliminasi
a + 2b = 17
a + 8b = 47
----------------------- -
-6b = -30
b = 5
a = a + 2(5) = 17
a = a + 10 =17
a= 17-10 = 7

U27
= 7 + (27-1) 5
= 7 + 26(5)
= 7 + 130
= 137

b = [tex] \frac{ U_{9} - U_{3}}{9 - 3} [/tex]
b = [tex] \frac{30}{6} [/tex]
b = 5

U3 = a + (n-1)b
17 = a + (3-1)5
17 = a + 10
a = 17 - 10
a = 7

U27 = 7 + (27 - 1)5
U27 = 7 + 26.5
U27 = 7 + 130
U27 = 137