Here is a labeled equation $\text{(1)}$: $$\begin{array}{}\text{(1)}& \frac{x+1}{\sqrt{1-x^2}}\end{array}$$ and another Equation $$\begin{array}{}& \frac{1}{3}\cdot \sum _{i=1}^n{x}^3\end{array}$$ This is equation test $$\begin{array}{}\text{(2)}& f(x)={\displaystyle \frac{a{x}^2+bx+c}{e^{x+2}}}\end{array}$$ This is an alignment test: $$\begin{array}{rl}x& =y_1-y_2+y_3-y_5+y_8-\dots \\ & y=y(0)y^{\prime }\text{by Axiom 1.}\\ & =\text{by Eq. }\text{(1)}\\ & =y^{\prime }\times y^{\frac{n}{2}}\end{array}$$