Basic reference of LaTeX environments that are useful to me. For now, these are limited to those that I have found useful for this web site.
align*
\begin{align*}
y & = 2x + 5 \\
y & = 3x - 1
\end{align*}\[\begin{align*} y & = 2x + 5 \\ y & = 3x - 1 \end{align*}\]
cases
\[
x_{n+1} = \begin{cases}
3 x_n + 1 & \text{if $x_n$ is odd} \\
\frac{x_n}{2} & \text{if $x_n$ is even}
\end{cases}
\]\[ x_{n+1} = \begin{cases} 3 x_n + 1 & \text{if $x_n$ is odd} \\ \frac{x_n}{2} & \text{if $x_n$ is even} \end{cases} \]