Using Equation References

Here is a labeled equation: $$x+1\over\sqrt{1-x^2}\label{ref1}$$ with a reference to ref1: \ref{ref1}, and another numbered one with no label: $$x+1\over\sqrt{1-x^2}$$

This one uses \nonumber: $$x+1\over\sqrt{1-x^2}\nonumber$$

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Here's one using the equation environment: \begin{equation} x+1\over\sqrt{1-x^2} \end{equation} and one with equation* environment: \begin{equation*} x+1\over\sqrt{1-x^2} \end{equation*}

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This is a forward reference [\ref{ref2}] and another \eqref{ref2} for the following equation: $$x+1\over\sqrt{1-x^2}\label{ref2}$$

More math: $$x+1\over\sqrt{1-x^2}$$

Here is a ref inside math: \(\ref{ref2}+1\) and text after it.

\begin{align} x & = y_1-y_2+y_3-y_5+y_8-\dots && \text{by \eqref{ref1}} \\ & = y'\circ y^* && \text{(by \eqref{ref3})} \\ & = y(0)\, y' && \text {by Axiom 1.} \end{align}

Here's a bad ref [\ref{ref4}] to a nonexistent label.

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An alignment: \begin{align} a & = b\label{ref3} \\ & = c+d \end{align} and a starred one: \begin{align*} a &= b \\ &= c + d \end{align*}