The solution of the FirstOrder DifferentialEquation, 

  dK/dt = K*x

  ->

  x(t) = x(0)*e^(K*t)

Represents a lot of phenomena. Inductors, Capacitors and Resistors
have this mathematical form, which is why AnalogComputers can model
the RealWorld using ElectricalCircuits. HigherOrder DifferentialEquations
can be simplified to FirstOrder.

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SeeAlso: ControllabilityAndObservability