suku ke - 16 dari barisan 12, 20, 28, 36

◎ a = 12
◎ b = U2 - U1 = 20 - 12 = 8

U16 = a + 15b
U16 = 12 + 15 (8)
U16 = 12 + 120
U16 = 132

U60 = a + 59b
U60 = 12 + 59 (8)
U60 = 12 + 472
U60 = 484

a=12
b=8
n=16
Un=a+(n-1)b =12+(16-1)8 = 12+ (15)8 = 12+120 = 132