Examine the story problem or situation and determine the rate at which the principal value varies. For example, when traveling in a taxicab there is often a per-mile charge. The principal value is the number of miles traveled whereas the rate is the price per mile.
Determine if there are minimal values associated with the function. Continuing with the taxicab example, there is often a minimum charge applied to the total transit cost that is added to the final value of the price multiplied by the number of miles driven.
Set the product of the rate of change and the principal value, most commonly represented by the letter "x," added to the minimum cost equal to f (x). The notation f (x) is spoken " f of x" and is not represented by a capital F. The resulting equation is the rule for the linear functions being examined.