\begin{equation} \begin{aligned} a &= b + c \\ &= d + e + f + g \\ &= h + i \end{aligned} \end{equation}

\frac{\partial u}{\partial t} = h^2 \left( \frac{\partial^2 u}{\partial x^2} + \frac{\partial^2 u}{\partial y^2} + \frac{\partial^2 u}{\partial z^2}\right)

\begin{bmatrix} 1 & 1 & 1 & 1 \\ 1 & 1 & 1 & 1 \\ 1 & 1 & 1 & 1 \\ 1 & 1 & 1 & 1 \\ \end{bmatrix}

P\left ( x, y \right ) =\left ( r\textbf{cos}(\alpha ), r\mathbf{sin}(\alpha ) \right ) \\ P(x', y') = \left ( r\textbf{cos}(\alpha+\Theta ), r\mathbf{sin}(\alpha+\Theta ) \right )