suku ke -20 barisan tersebut adalah

b = 27-7 / 8-3 = 20/5 = 4
U3= a +2.4
7= a+8
a = -1
U20 = -1 + 19.4 = 75

U3 = 7
U8 = 27

b = (27 - 7) / (8 - 3)
b = 20/5
b = 4

Un = a + (n - 1) b
7 = a + (3 - 1) 4
7 = a + 8
a = 7 - 8
a = -1

Un = a + (n - 1) b
U20 = -1 + (20 - 1) 4
U20 = -1 + 76
U20 = 75