1. Dik : 5, 10, 15, 20..., 85 Dit :N.....? 2. Dik : 20, 15, 10, 5 ...? Dit: U10 dan Un

1. Dik, a = 5
b = U2-U1
b = 10 - 5 = 5
Un = a + (n-1) b = 85
= 5 + (n-1) 5 = 85
= 5 + 5n - 5 = 85
= 5n = 85
n = 85/5
n = 17

2. Dik, a = 20
b = 15 - 20
b = -5
Un = a + (n-1) b
U10 = 20 + (10-1) x -5
= 20 + (-45)
= -25