LyX ⇒ Help with aligning math formula and numbering

[meho_r]

OK, here's one way:

1. Insert AMS align Environtment (Insert > Math > AMS align Environment)
2. In the first placeholder type the left part of the equation, including the equal sign
3. In the second placeholder type the rest of the first line, then press Ctrl+Return
4. Leave the first placeholder on the second line empty, and type in the second one the rest of the second line. Do same for all subsequent lines.
5. To help indent the second and other lines, use phantom command, just type in the front of + from the beginning of the second (and other) line(s): \phantom{ and then type in the placeholder which will appear: Ctrl+Space then = and then again Ctrl+Space. This will create an empty space equal to Space+=+Space.
6. To number a particular line, click in that line, then Edit > Math > Number This Line. Alternatively, you can use Insert > Label to label the equation (and the line in which the cursor is placed will be numbered) so you can reference to it in the text.

In the attachment is an example file (you'll need LyX 2.0.0rc3 to open it).