Recursive

Step 1. Define the first term.

Step 2. Find the pattern to get from one term to the next.

12 - 3 = 9
9 - 3 = 6
6 - 3 = 3
3 - 3 = 0

Step 3. Write a recursive function to represent this pattern.

Step 4. Put the two parts together into one recursive formula.

The recursive formula is: