Answer:
nth term = 21 - 3n
Step-by-step explanation:
18,15,12,9....
This is an arithmetic sequence.
a= first term = 18
Common difference = d = second term - first term
d = 15 - 18
d = -3
nth term = a + (n-1)d
= 18 + (n-1)*(-3)
= 18 + n*(-3) - 1*(-3)
= 18 - 3n + 3
= 21 - 3n
