Diketahui barisan 3, 5, 7, 9, 11,… tentukan suku ke-21 barisan tersebut​

N = 21
a = 3
b = 5-3 = 2

rumusnya : Un = a + ( n – 1 )b

Maka, U21 = 3 + ( 21 – 1 )2
U21 = 3 + (20)2
U21 = 3 + 40
U21 = 43