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R_\theta = 
    \begin{bmatrix}
        \cos \theta &          -  \sin \theta \\
        \sin \theta & \phantom{-} \cos \theta 
\end{bmatrix}

$$R_\theta = \begin{bmatrix} \cos \theta & -\sin \theta \\ \sin \theta & \phantom{-} \cos \theta \end{bmatrix}$$

e^{-a|x|} =
\begin{cases}
    e^{ax}  & \text{if } x <    0 \\
    e^{-ax} & \text{if } x \geq 0
\end{cases}

$$e^{-a|x|} = \begin{cases} e^{ax} & \text{if } x < 0 \\ e^{-ax} & \text{if } x \geq 0 \end{cases}$$

$$\nabla \times \overrightarrow{\mathbf{B}} - \frac{1}{C} \frac{\delta \overrightarrow{\mathbf{E}}}{\delta t} = 4\pi \rho$$

$${\cal H}=\mathcal{H}$$