190514

\[\begin{equation} e=mc^2 \end{equation}\label{eq1}\]

\[\begin{equation} \begin{aligned} a &= b + c \\ &= d + e + f + g \\ &= h + i \end{aligned} \end{equation}\label{eq2}\]

\[\begin{align} -4 + 5x &= 2+y \nonumber \\ w+2 &= -1+w \\ ab &= cb \end{align}\]

\[x+1\over\sqrt{1-x^2} \tag{i}\label{eq_tag}\]