Actually, I tested this, and it is ok to have it start on the same line as the ``.. math::`` directive, but then the next lines have to be indented.  E.g.,
```
.. math:: P(x,y) ... y^n
    + c_{1_1}xy ...
```
Whereas in the current code, the ``+ c`` part is at the same indentation level as ``.. math::``

For readability, I'd still say it's better to have it offset like this the above, though.