suatu barisan aritmetika U5=124 dan U9=20 nilai U7 adalah

U5 = 124
U5 = a + 4b = 124

U9 = 20
U9 = a + 8b = 20

4b = U9 - U5
4b = 20 - 124
4b = -104
b = -104/4
b = -26

a + 4b = 124
a + 4(-26) = 124
a + -104 = 124
a = 124 + 104
a = 228

U7 = a + 6b
= 228 + 6.(-26)
= 228 - 156
= 72