\begin{definition}[Definition:Quadratic Equation]
A '''quadratic equation''' is a polynomial equation of the form:
:$a x^2 + b x + c = 0$
such that $a \ne 0$.
From Solution to Quadratic Equation, the solutions are:
:$x = \dfrac {-b \pm \sqrt {b^2 - 4 a c} } {2 a}$
\end{definition}