Exercise 98 Page 341

To write an explicit equation for the sequence based on the graph, we must first determine if this is an arithmetic sequence or a geometric sequence. By determining the vertical difference between consecutive terms we can tell if this is an arithmetic sequence. If it is, the difference between consecutive terms will be constant.

Since there is no common difference between consecutive terms, this is not an arithmetic sequence. Therefore, it's likely a geometric sequence. We know this is the case if there is a common ratio between consecutive terms.

There is a common ratio between consecutive terms. By substituting $r=3$ and $a_1=12,$ we can write our explicit equation.