190514

$$\begin{equation} e=mc^2 \end{equation}\label{eq1}$$ $$\begin{equation} \begin{aligned} a &= b + c \\ &= d + e + f + g \\ &= h + i \end{aligned} \end{equation}\label{eq2}$$ $$\begin{align} -4 + 5x &= 2+y \nonumber \\ w+2 &= -1+w \\ ab &= cb \end{align}$$ $$x+1\over\sqrt{1-x^2} \tag{i}\label{eq_tag}$$