The second method of Lyapunov is used to validate Aizerman\´s conjecture for the class of third-order nonlinear control systems described by the following differential equation:

In this case, the stability of the nonlinear system may be inferred by considering an associated linear system in which the nonlinear function

is replaced by

. If the linear system is asymptotically stable for

, then the nonlinear system will be asymptotically stable in-the-large for any

for which

The Lyapunov function used to prove this result is determined in a straightforward manner by considering the physical behavior of the system at the extreme points of the allowable range of

.