Ref

Ref is example of numbering of equations and referencing to the equation number.

test \begin{equation} x+1\over\sqrt{1-x^2}\label{ref2} \end{equation}

\begin{equation} \mathrm{e}^{\mathrm i \pi}+1=0 \label{e} \end{equation}

\begin{eqnarray} 123 \label{h} \end{eqnarray}

Do you like equation [\ref{ref2}]?

Do you like equation (\ref{e})?

How about \ref{h}?

References

https://www.tuhh.de/MathJax/test/sample-eqrefs.html