ABSTRACT
This chapter presents some wide classes of first order differential equations that can be solved at least implicitly. It considers a class of differential equations for which solutions can be determined by integration. In calculus, points where the derivative vanishes are called the critical points. Therefore, sometimes equilibrium solutions are called the critical points of the slope function. The chapter discusses a hollow iron ball in steady state heat; that is, the temperature is independent of time, but it may be different from point to point. The bone marrow of a human constantly produces red blood cells because they have a finite life span. The oxygen level in kidney tissue determines the production of erythropoietin (Epo), and the level of Epo is proportional to the rate of red blood cell production. This means that the oxygen level is inversely proportional to the rate of erythrocyte production.
