If you want to control this individually, one approach would be to use
<div style="margin: 1em 0; text-align:left">
\(\displaystyle{ ... math ... }\)
</div>
which makes an in-line equation using the displaystyle typesetting
rules, and the surrounding div controls the alignment. That should
work provided you aren't using \tag.
If you really need to have two different types of alignment, you can
typeset the first set of equations, then change displayAlign and
typeset the second set. Of they all appear together in one group, you
can set the element array in your configuration file to include the
names of the containers for the centered equations (see http://www.mathjax.org/docs/1.1/options/hub.html)q
, and then
<script>
MathJax.Hub.Queue(function () {
MathJax.Hub.Configure({displayAlign:"left"});
MathJax.Hub.Typeset(["div1","div2","div3"]);
});
</script>
to typeset the contents of the elements with ids div1, div2, and div3
aligned to the left.
Davide