What does the sales force estimation method rely on for forecasting future sales?

Bottom-up method

Explanation:

The bottom-up method is a good way to promote sales forecast, especially if it is desirable to make a monthly forecast. Through this method, the trader can predict how many units he will sell in the month. This is done by calculating the average price of each unit, which will be multiplied by the number of units of the product, thus giving an estimated number of monthly sales.

to answer your question:

f(x)= a^x.  if x=0, f(x)=1  if x=1, f(x)=a  if x=1, f(x)=a^a