I thought you had the same question but then with equation instead of Eq. Package amsmath this is used because of align provides an easy way to add the. Either number the AMSmath environments as LaTeX would or number all displayed equations the example above uses AMS-style numbering.
Remember that numberwithin doesnt come from LaTeX.
For example the code intlimits_ -infty infty e -x 2 dx sqrt pi yields. Automatic equation numbering on the right of the formula Hello. Highlight the equation table. We can also edit the equation label and use Eq instead of just a number.