diketahui barisan aritmatika u4=19 dan u9=39 suku ke 41 adalah

Un = a + ( n - 1) b

U4 = a + 3b = 19
U9 = a + 8b = 39
--------------------------(-)
- 5b = - 20
b = 4

a + 3b = 19
a + 3(4) = 19
a + 12 = 19
a = 19 - 12
a = 7

U41 = a + 40b
= 7 + 40(4)
= 7 + 160
= 167