\begin{matrix} a_{11} & a_{12} & a_{13}\\ a_{21} & a_{22} & a_{23} \end{matrix}
$$\begin{matrix} a_{11} & a_{12} & a_{13}\\ a_{21} & a_{22} & a_{23} \end{matrix}$$
\begin{pmatrix}p_{11}&p_{12}\\p_{21}&p_{22}\end{pmatrix}, \begin{bmatrix}b_{11}&b_{12}\\b_{21}&b_{22}\end{bmatrix}, \begin{Bmatrix}B_{11}&B_{12}\\B_{21}&B_{22}\end{Bmatrix}, \begin{vmatrix}v_{11}&v_{12}\\v_{21}&v_{22}\end{vmatrix}, \begin{Vmatrix}V_{11}&V_{12}\\V_{21}&V_{22}\end{Vmatrix}
$$ \begin{pmatrix}p_{11}&p_{12}\\p_{21}&p_{22}\end{pmatrix}, \begin{bmatrix}b_{11}&b_{12}\\b_{21}&b_{22}\end{bmatrix}, \begin{Bmatrix}B_{11}&B_{12}\\B_{21}&B_{22}\end{Bmatrix}, \begin{vmatrix}v_{11}&v_{12}\\v_{21}&v_{22}\end{vmatrix}, \begin{Vmatrix}V_{11}&V_{12}\\V_{21}&V_{22}\end{Vmatrix} $$
\theta(x)=\begin{cases}0&(x<0)\\1&(x\ge 0)\end{cases}
$$ \theta(x)=\begin{cases}0&(x<0)\\1&(x\ge 0)\end{cases} $$
\begin{align}\cos 2x &= \cos^2x-\sin^2x\\ &= 2\cos^2x-1\\ \frac{\cos 2x+1}{2} &= \cos^2x \end{align}
$$ \begin{align}\cos 2x &= \cos^2x-\sin^2x\\ &= 2\cos^2x-1\\ \frac{\cos 2x+1}{2} &= \cos^2x \end{align} $$
A\sqrt{B}C, A\substack{B}C, A\underset{B}C, A\not{B}C
$A\sqrt{B}C, A\substack{B}C, A\underset{B}C, A\not{B}C$
$\color{GreenYellow}{AAA}\overset{a}{\color{blue}x} $
$\text{text}, \textit{textit} \textbf{textbf} \textrm{textrm} \texttt{texttt} \textsf{textsf} \emph{emph} \hbox{hbox} \mbox{mbox}$
$\mathrel{Z}$
\alpha \beta \gamma \delta \epsilon \varepsilon \zeta \eta \vartheta \theta \iota \kappa \varkappa \lambda \mu \nu \pi \varpi \rho \varrho \sigma \varsigma \tau \upsilon \phi \varphi \chi \psi \omega \xi \digamma \Gamma \Delta \Theta \Lambda \Pi \Sigma \Upsilon \Phi \Psi \Omega \Xi
$\alpha \beta \gamma \delta \epsilon \varepsilon \zeta \eta \vartheta \theta \iota \kappa \varkappa \lambda \mu \nu \pi \varpi \rho \varrho \sigma \varsigma \tau \upsilon \phi \varphi \chi \psi \omega \xi \digamma \Gamma \Delta \Theta \Lambda \Pi \Sigma \Upsilon \Phi \Psi \Omega \Xi$