We will use the slope of economic functions to define a number of important economic variables. As examples,

a. The change in cost resulting from a change in the level of output is called the marginal cost of production. It is measured by the slope of the total cost function.

b. The change in consumption resulting from a change in the level of income is called the marginal propensity to consume. It is measured by the slope of the consumption function.

Functions may have different slopes at different points.

Linear functions have the same slope at all points along the graphs of the functions.