Figures 7.4e and f show the curves based on the linear form. Note that the law of diminishing marginal returns has been eliminated. Each additional unit cost is the constant, b.Thus, this specification of the cost curve exhibits strictly constant marginal costs. This type of analysis does not appeal intuitively to an economist, who knows that if units of a variable factor are continually added to a fixed factor (plant), somewhere at higher production levels unit costs must rise