Here is a labeled equation: $$x+1\over\sqrt{1-x^2}\label{eq1}$$ and another Equation $$\frac{1}{3}\cdot\sum_{i=1}^{n} x^{3} \nonumber$$ This is equation test \begin{equation} This is an alignment test: \begin{align*} x&=y_1-y_2+y_3-y_5+y_8-\dots \\ &=y(0) y'\; \tex{by Axion 1.} \nonumber\\ &= \tex{by Eq. \eqref{eq1}}\nonumber \\ &= y'\times y^\frac{n}{2} \\ \end{align*}