The domain of the function is the set of "x" values that the function can assume. However, when we talk about practical domain, we want to take into consideration the use of the function. In this function, "x" is the number of payments He made. This means that:
- We can't have a negative number of payments, so "x" has to be positive.
- We can't make a fraction of a payment, so "x" must be a whole number.
- We can't make more payments than the amount necessary for the loan, so we can't have "x" greater than:
Putting these into consideration, the practical domain of the function "f" is "All whole numbers from 0 to 74".