Past exam of the mathematics course of the University of Cambridge 2015 ia Paper 2 2B Solution Created 2026-09-24 Updated 2026-10-06
The equilibrium points are . To obtain the other solutions of this separable differential equation without losing their signs, set on an interval where . Then , so . Therefore all real solutions areon intervals where . This family includes when . For a prescribed finite nonzero , and , so the solution exists for all future time. The cubic logistic differential equation hasThese are the only possible limits. The sign cannot change by uniqueness, and the denominator tends to one. A nonzero initial condition producing a constant solution is ; also works. The central equilibrium point is unstable and the two outer equilibrium points attract solutions from their respective half-lines.