淘题库这是一篇测试性的文章，我设置了头图和摘要\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)\(\left(\begin{array}{c|c} 1 & 2 \\ \hline 3 & 4 \end{array}\right)\)文字类的东西意向\(\sum_{i=0}^{n}i^2\)不太好弄的\(y = \left\{ \begin{array}{ll} a & \textrm{if $d>c$}\\ b+x & \textrm{in the morning}\\ l & \textrm{all day long} \end{array} \right.\)\(\mathbf{X} = \left( \begin{array}{ccc} x_{11} & x_{12} & \ldots \\ x_{21} & x_{22} & \ldots \\ \vdots & \vdots & \ddots \end{array} \right)\)发\(\begin{matrix}1 & 2\\3 &4\end{matrix}\)\(\begin{pmatrix}1 & 2\\3 &4\end{pmatrix} \begin{bmatrix}1 & 2\\3 &4\end{bmatrix} \begin{Bmatrix}1 & 2\\3 &4\end{Bmatrix} \begin{vmatrix}1 & 2\\3 &4\end{vmatrix} \begin{Vmatrix}1 & 2\\3 &4\end{Vmatrix}\)