How do I add an math equation system using Formula feature? That is, an extandable bracket to the left side of the equations… It seems there isn’t any possibility.

It seems like it does not exist in LibreOffice Math (yet hopefully). But yes - mentioned workaround works. This moment is not very comfortable to explain to regular user, that she/he have to go into code window and change *rbrace* into *none*. Also the experimental feature, which allows edit formula directly in show area, should be enabled by default. This can be turned on in Tools->Settings->Advanced menu.

For example two formula systems - one without alignment and second one with alignment:

left lbrace { binom { 3 x + y = 4 } { 2 x - y = 1 } } right none

left lbrace alignl { binom { 3 x - 2 y = 4 } { x + y = 3} } right none

This means, that if equations have unequal length, then alignment would be necessary.

The stack could be used if there is more than 2 equations needed to bind into system.

I checked the link; there are some notes at the bottom of the page regarding what I asked but I didn’t quite understand how to do it. Anyhow, I found something in the Elements panel name stack which does the job. The final formula is something like left lbrace stack{a # ab # abc} right none