\begin{matrix} x = \frac{- b \pm \sqrt{b^{2} - 4 a c}}{2 a} \\ a^{2} + b^{2} = c^{2} \\ e^{i π} + 1 = 0 \\ \sum_{k = 1}^{n} k = \frac{n (n + 1)}{2} \end{matrix}