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

${\vec{\nabla} \times \vec{F}}.$ =

            ${\left( \frac{\partial F_z}{\partial y} - \frac{\partial F_y}{\partial z} \right) \mathbf{i} + \left( \frac{\partial F_x}{\partial z} - \frac{\partial F_z}{\partial x} \right) \mathbf{j} + \left( \frac{\partial F_y}{\partial x} - \frac{\partial F_x}{\partial y} \right) \mathbf{k}}.$

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

$f(a) = {\frac{1}{2\pi i} \oint\frac{f(z)}{z-a}dz}.$