Jika U4 = 3, U6-U1=5, maka awal dan bedanya adalah...

a+3b=3
a+5b-a=5..5b=5..b=1
Jadi a+3.1=3...a=0

U4 = a + (4-1)b = 3


U6 - U1 = 5
a + (6-1)b - a = 5
6b - b = 5
5b = 5
b = 1

subsitusi nilai b ke U4

U4 = 3
a + 3b = 3
a + 3(1) = 3
a + 3 = 3
a = 3-3
a = 0 <<===