Exercise 55 Page 280

When a sequence is arithmetic, the difference between two consecutive terms is constant. Examining our sequence we can see that this is the case. Since the difference between consecutive terms is constant and equal to $\text{-}4,$ we have an arithmetic sequence with common difference $\text{-}4.$ We will use this information to write both the recursive and the explicit formula.

Recursive Formula

Let's recall the general form of the recursive formula for an arithmetic sequence.