Tentukan Suku ke 18 dari barisan berikut: 40,37,34,31,28...

a = 40
b = U2-U1 = 37-40 = -3

Un = a + (n-1)b
U18 = 40 + (18-1)(-3)
U18 = 40 + 17(-3) = 40 - 51 = -11

U18 = a + (n-1) × b
= 40 + ( 18-1) × -3
= 40 + (-51)
= -11