Find the nth term rule for 18,15,12,9

an = a+(n-1) d

this is the rule

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