This is an example:\(x+1=\frac{x}{3}\)
/begin{equation*}
y=\frac{\sum_{i=0}^{n}(x_{i}^{2})}{x_{i}}
\end{equation*}
This is Equation \ref{eq:1}.
Here is a labeled eq:$$x+1\over\sqrt{1-x^2}\label{eq:1}$$
/begin{align}
x &=y_1-y_2+y_3-y_5-\dots
&& \text{ by \eqref{eq:1}} \\
&=y'\circ y^* && \text{(by \eqref{eq:1})}}\\
& y(0) y' * \text{by Axiom 1.}
\end{align}
This is an another Eq. \ref{ref3}.
\begin{align*}
a &=b \\
y &=c+d
\end{align*}