try to use split environment

src/8_differential_equations_2.md

@@ -55,11 +55,13 @@ $$y_{1} = y, \ y_{2} = y', \ \cdots, \ y_{n} = y^{(n-1)}.$$
 
 Then, the differential equation can be re-written as
 
-$$y_1 ' = y_2$$
-$$y_2 ' = y_3$$
-$$ \vdots $$
-$$y_{n-1} ' = y_{n}$$
-$$y_{n} ' = - a_{0} y_{1} - a_{1} y_{2} - \cdots - a_{n-1} y_{n}.$$
+$$\begin{split}
+y_1 ' = & y_2 \\
+y_2 ' = & y_3 \\
+\vdots & \\
+y_{n-1} ' = & y_{n} \\
+$$y_{n} ' = & - a_{0} y_{1} - a_{1} y_{2} - \cdots - a_{n-1} y_{n}.
+\end{split}$$
 
 Notice that together these $n$ equations form a linear first order system, the 
 first $n-1$ equations of which are trivial. Note that this trick can be used to