Diketahui barisan aritmatika dengan U5=21 dan U10= 41. Tentukan U56

U10 = a + 9b = 41
U5 = a + 4b = 21
------------------------  -
5b = 20
b = 20/5
b = 4

a + 4b = 21
a + 4.4 = 21
a + 16 = 21
a = 21 - 16
a = 5

U56 = a + 55b
U56 = 5 + 55.4
U56 = 5 + 220
U56 = 225

a + 4b = 21
a + 9b = 41 _
-5b = -20
b = -20/-5
b = 4

a + 4b = 21
a + 4.4 = 21
a + 16 = 21
a = 21 - 16
a = 5

b = 4 , a = 5 , n = 56

Un = a + (n - 1)b
U56 = a + 55b
U56 = 5 + 55.4
U56 = 5 + 220
U56 = 225