Q:

left align an alignedat environment

now I am trying to get this output aligned to the left of my document

This is the code that I am using to achieve it :
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{flalign*}
    \begin{alignedat}{10}
    &a &&\phantom{+ b} &&\phantom{+ c} &&\phantom{+ d} &&\phantom{+ e} &&\phantom{+ f} &&\phantom{+ g} &&\phantom{+ h} &&\phantom{+ i} &&= 0 \\
    &\phantom{a} &&\phantom{+}b &&\phantom{+ c} &&+ d &&\phantom{+ e} &&\phantom{+ f} &&\phantom{+ g} &&\phantom{+ h} &&\phantom{+ i} &&= 0 \\
    &\phantom{a} &&\phantom{+ b} &&\phantom{+} c &&\phantom{+ d} &&\phantom{+ e} &&\phantom{+ f} &&+ g &&\phantom{+ h} &&\phantom{+ i} &&= 0 \\
    &\phantom{a} &&\phantom{+}b &&\phantom{+ c} &&+ d &&\phantom{+ e} &&\phantom{+ f} &&\phantom{+ g} &&\phantom{+ h} &&\phantom{+ i} &&= 0 \\
    &\phantom{a} &&\phantom{+ b} &&\phantom{+ c} &&\phantom{+ d} &&\phantom{+} e &&\phantom{+ f} &&\phantom{+ g} &&\phantom{+ h} &&\phantom{+ i} &&= 0 \\
    &\phantom{a} &&\phantom{+ b} &&\phantom{+ c} &&\phantom{+ d} &&\phantom{+ e} &&\phantom{+} f &&\phantom{+ g} &&+ h &&\phantom{+ i} &&= 0 \\
    &\phantom{a} &&\phantom{+ b} &&\phantom{+} c &&\phantom{+ d} &&\phantom{+ e} &&\phantom{+ f} &&+ g &&\phantom{+ h} &&\phantom{+ i} &&= 0 \\
    &\phantom{a} &&\phantom{+ b} &&\phantom{+ c} &&\phantom{+ d} &&\phantom{+ e} &&\phantom{+} f &&\phantom{+ g} &&+ h &&\phantom{+ i} &&= 0 \\
    &\phantom{a} &&\phantom{+ b} &&\phantom{+ c} &&\phantom{+ d} &&\phantom{+ e} &&\phantom{+ f} &&\phantom{+ g} &&\phantom{+ h} &&\phantom{+} i &&= 0
    \end{alignedat}
\end{flalign*}
\end{document}

This is what I am getting though :

Could you help me get it to the left of the page as desired?
Any help would be greatly appreciated, thanks in advance.

A:

This doesn't use flalign but I hope that it helps!
\documentclass{article}
\begin{document}
$\begin{array}{cccccccccc}
    a &   &   &    &   &   &    &    &   &=0 \\
      & b &   &+\;d&   &   &    &    &   &=0 \\
      &   & c &    &   &   &+\;g&    &   &=0 \\
      & b &   &+\;d&   &   &    &    &   &=0 \\
      &   &   &    & e &   &    &    &   &=0 \\
      &   &   &    &   & f &    &+\;h&   &=0 \\
      &   & c &    &   &   &+\;g&    &   &=0 \\
      &   &   &    &   & f &    &+\;h&   &=0 \\
      &   &   &    &   &   &    &    & i &=0
\end{array}$
\end{document}

One advantage of this is that you can use it in the same line with your text (though I don't use that advantage usually).

