Suatu Barisan aritmatika dengan U3 = 12 dan U9 = 20 . Tentukan nilai U7 !

U3 = a + 2b = 12
u9 = a + 8b = 20
_____________ –
-6b = -8
b = 4/3

a + 2b = 12
a + (8/3) = 12
a = 12 – 8/3
a = (36-8)/3
a = 28/3

U7 = a + 6b
U7 = (28/3) + (24/3)
U7 = 52/3
U7 = 17,33