User:Eliasrg/Math/pq-formula

$$ \begin{align} x^2 + p x + q & = 0\\ x^2 + p x + \left ( \frac{p}{2} \right )^2 & = \left ( \frac{p}{2} \right )^2 -q\\ \left (x + \frac{p}{2} \right )^2 & = \left ( \frac{p}{2} \right )^2 -q\\ x + \frac{p}{2} & = \pm \sqrt{\left ( \frac{p}{2} \right )^2 -q}\\ x & = -\frac{p}{2} \pm \sqrt{\left ( \frac{p}{2} \right )^2 -q}\\ \end{align} $$