Documentclassa4paper10ptleqnoarticle begindocument begineqnarray 7x 4y 0 2x - 5y 0 endeqnarray enddocument Which gives. The label command should be added after the counter number for the section has been generated. Again use to toggle the equation numbering.
LaTeX assumes that each equation consists of two parts separated by a.
For example in the case of an article in A4 format of size 10 points. We can change this to Roman numerals andor letters. Also that each equation is separated from the one before by an. For example the code intlimits_-inftyinfty e-x2 dx sqrtpi yields.