In their analysis they used calculus and solved the system of equations resulting from the first-order conditions.
They did not explicitly identify the two distinct cases we examine here. Our analysis is based
entirely on an algebraic approach.
In addition to the fact that it is of interest to demonstrate how a relatively complex model can be fully analyzed without derivatives, we obtain the explicit identification of the two cases, a result that does not appear as easy to do by using calculus.
First we examine the EOQ model and at the end present the results for the EPQ.