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} f(x)=\dfrac{ax^2+bx+c}{e^{x+2}} \end{equation} This is an alignment test: \begin{align*} x&=y_1-y_2+y_3-y-5+y_8-\dots \\ &= y(0) y' \; \text{by Axiom 1.} \nonumber\\ &= \text{by Eq.\eqref{eq1}\nonumber\\ &= y'\times y^\frac{n}{2} \\ \end{align*}