diketahui barisan aritmetika dg suku ke-4=24 dan suku ke-10=42. suku ke-30 barisan tersebut adalah?

U4 = a+3b = 24
U10 = a+9b = 42
_____________ -
-6b = -18
b = 3
a+3b = 24
a+3(3)=24
a+9=24
a = 24-9
a = 15

U30 = a+19b
= 15+19(3)
= 15+57
= 72

U4 =U1 + 3b = 24
U10 = U1 + 9b = 42
---------------------------(-)
========>- 6b = -18
========> b = 3

U4 = U1 + 3b
24 = U1 + 3(3)
24 = U1 + 9
U1 = 24 - 9
U1 = 15

U30 = U1 + (30-1) 3
U30 = 15 + 29*3
U30 = 15 + 87
U30 = 102

semoga membantu ^_^