When $a \ne 0$, there are two solutions to $ax^2 + bx + c = 0$ and they are $x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$

$\sum_{i=0}^n i^2 = \frac{(n^2+n)(2n+1)}{6}$

$\sum_{i=0}^n i^2 = \frac{(n^2+n)(2n+1)}{6}$

$x = {-b \pm \sqrt{b^2-4ac} \over 2a}$

$f(x) = \int_{-\infty}^\infty\hat f(\xi)\,e^{2 \pi i \xi x}\,d\xi$