math

$$ e^{i\pi} - 1 = 0 $$

e^{i\pi} - 1 = 0

$$ \tan (\alpha \pm \beta) = \frac{\tan \alpha \pm \tan \beta}{1 \mp \tan \alpha \tan \beta} \hspace{1em} (複号同順) $$

\tan (\alpha \pm \beta) = \frac{\tan \alpha \pm \tan \beta}{1 \mp \tan \alpha \tan \beta} \hspace{1em} (複号同順)

$$ \begin{align} \sum_{k=1}^{n} k &= 1 + 2 + \dots + n \\ &= \frac{1}{2}n(n + 1) \end{align} $$ <code> \begin{align} \sum_{k=1}^{n} k &= 1 + 2 + \dots + n \\ &= \frac{1}{2}n(n + 1) \end{align} </code>

$$ \left( \begin{array}{ccccc} a_{11} & \cdots & a_{1i} & \cdots & a_{1n} \\ \vdots & \ddots & & & \vdots \\ a_{i1} & & a_{ii} & & a_{in} \\ \vdots & & & \ddots & \vdots \\ a_{n1} & \cdots & a_{ni} & \cdots & a_{nn} \end{array} \right) $$

\left(
\begin{array}{ccccc}
a_{11} & \cdots & a_{1i} & \cdots & a_{1n}\
\vdots & \ddots & & & \vdots \
a_{i1} & & a_{ii} & & a_{in} \
\vdots & & & \ddots & \vdots \
a_{n1} & \cdots & a_{ni} & \cdots & a_{nn}
\end{array}
\right)