bubee_wechat

$$\begin{cases} a_{11}x_1&+&a_{12}x_2&+&\cdots&+a_{1n}x_n&=&b_1\\ &&&&\vdots\\ a_{n1}x_1&+&a_{n2}x_2&+&\cdots&+a_{nn}x_n&=&b_n& \end{cases}$$