#### The Quadratic Formula

\[x = {-b \pm \sqrt{b^2-4ac} \over 2a}.\]#### Cauchy’s Integral Formula

\[f(a) = \frac{1}{2\pi i} \oint\frac{f(z)}{z-a}dz\]#### Double angle formula for Cosines

\[\cos(θ+φ)=\cos(θ)\cos(φ)−\sin(θ)\sin(φ)\]#### Gauss’ Divergence Theorem

\[\int_D ({\nabla\cdot} F)dV=\int_{\partial D} F\cdot ndS\]#### Curl of a Vector Field

\[\vec{\nabla} \times \vec{F} = \left( \frac{\partial F_z}{\partial y} – \frac{\partial F_y}{\partial z} \right) \mathbf{i}\left( \frac{\partial F_x}{\partial z} – \frac{\partial F_z}{\partial x} \right) \mathbf{j} + \left( \frac{\partialF_y}{\partial x} – \frac{\partial F_x}{\partial y} \right) \mathbf{k}\]