\begin{definition}[Definition:Quadratic Function]
A '''quadratic function''' is an expression of the form:
:$\map Q x := a_0 + a_1 x + a_2 x^2$
where $a_0, a_1, a_2$ are constants.
The domain of $x$ is usually defined as the real numbers $\R$ or the 
complex numbers $\C$.
\end{definition}