Pelajaran ttg suku barisan aritmatika

b= 4-1 = 3

Un= a+ (n-1)b

U10 = a+ 9b
=> 1+ 9(3) = 28

U20= a+ 19b
=> 1 + 19(3) = 58

U50 = a+ 49(b)
=> 1 + 49(3) = 148