\begin{definition}[Definition:Reduced Equation of Linear ODE with Constant Coefficients/First Order]
Consider the linear first order ODE with constant coefficients:
:$(1): \quad \dfrac {\d y} {\d x} + a y = \map Q x$
The equation:
:$\dfrac {\d y} {\d x} + a y = 0$
is the '''reduced equation''' of $(1)$.
\end{definition}