Tentukan Suku ke 10,20,dan 30 dan un! dengan caranya ya

a). 6,9,12,15,...
a = 6
b = 9-6 = 3
Un = a+(n-1) b
Un = 6+(n-1) 3
Un = 6+3n-3
Un = 3n+3

U10 = 3.10+3
U10 = 30+3
U10 = 33

U20 = 3.20+3
U20 = 60+3
U20 = 63

U30 = 3.30+3
U30 = 90+3
U30 = 93

b). 20,25,30,35,...
a = 20
b = 25-20 = 5
Un = a+(n-1) b
Un = 20+(n-1) 5
Un = 20+5n-5
Un = 5n+15

U10 = 5.10+15
U10 = 50+15
U10 = 65

U20 = 5.20+15
U20 = 100+15
U20 = 115

U30 = 5.30+15
U30 = 150+15
U30 = 165

c). 200,195,190,185,...
a = 200
b = 195-200 = -5
Un = a+(n-1) b
Un = 200+(n-1) (-5)
Un = 200-5n+5
Un = -5n+205

U10 = -5.10+205
U10 = -50+205
U10 = 155

U20 = -5.20+205
U20 = -100+205
U20 = 105

U30 = -5.30+205
U30 = -150+205
U30 = 55