Markdown 数学公式
当你需要在编辑器中插入数学公式时，可以使用两个美元符 $$ 包裹 TeX 或 LaTeX 格式的数学公式来实现。如：
一个简单的数学公式，求圆的面积：
$$
S=\pi r^2
$$
$$ S=\pi r^2 $$
其他公式：
$$
x \href{why-equal.html}{=} y^2 + 1
$$
$$ x \href{why-equal.html}{=} y^2 + 1 $$
$$
x = {-b \pm \sqrt{b^2-4ac} \over 2a}.
$$
$$ x = {-b \pm \sqrt{b^2-4ac} \over 2a}. $$
$$
\left [ – \frac{\hbar^2}{2 m} \frac{\partial^2}{\partial x^2} + V \right ] \Psi = i \hbar \frac{\partial}{\partial t} \Psi
$$
$$ \left [ – \frac{\hbar^2}{2 m} \frac{\partial^2}{\partial x^2} + V \right ] \Psi = i \hbar \frac{\partial}{\partial t} \Psi $$
Alternatively, inline math can be written by wrapping the formula with only a single $:
This is inline: $\mathbf{y} = \mathbf{X}\boldsymbol\beta + \boldsymbol\varepsilon$
This is inline: $\mathbf{y} = \mathbf{X}\boldsymbol\beta + \boldsymbol\varepsilon$
Note that Markdown special characters need to be escaped with a backslash so they are treated as math rather than Markdown. For example, * and _ become \* and \_ respectively.
同时也支持 HTML 属性，如：
$$
(x+1)^2 = \class{hidden}{(x+1)(x+1)}
$$
$$
(x+1)^2 = \cssId{step1}{\style{visibility:hidden}{(x+1)(x+1)}}
$$
$$ (x+1)^2 = \class{hidden}{(x+1)(x+1)} $$
$$ (x+1)^2 = \cssId{step1}{\style{visibility:hidden}{(x+1)(x+1)}} $$