trouble in using flalign (LaTeX)

Question

I am trying to put 3 equations with "=" signs aligned but also left aligned. I tried the following:

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\begin{flalign*}
RPC &= A+B\tilde{f} +C x  &\\
A   &= a+\eta             &\\
E   &= cte                &
\end{flalign*}

\end{document}

With this I get the stuff in the left and the "=" signs aligned. However, I also need A (in the second equation) and E (in the third equation) to be aligned to the R (in the first one)

Does anyone know how to get it?

thanks

Answer 1

What follows is not elegant but it does the trick:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{minipage}{0pt}

\begin{flalign*}

& RPC & &\mspace{-22.0mu} = A+B\tilde{f} +C x \

& A & &\mspace{-22.0mu} = a+\eta \

& E & &\mspace{-22.0mu} = cte

\end{flalign*}

\end{minipage}

\end{document}

Answer 2

I have tried all different combinations of &s and haven't found anything that works quite right. There's probably some better way of doing it, but you could just use \hphantom to make the A and E take roughly the same amount of space as RPC:

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\begin{flalign*}
RPC            & = A+B\tilde{f} +C x  \\
A\hphantom{PC} & = a+\eta \\
E\hphantom{PC} & = cte
\end{flalign*}

\end{document}

Answer 3

Thank you guys. This seems to produce somewhat good results:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{flalign*}

RPC\hphantom{AE} & \mspace{-30.0mu}= A+B\tilde{f} +C x & \

A \hphantom{RPCE} & \mspace{-30.0mu}= a+\eta &\

E \hphantom{RPCA} & \mspace{-30.0mu}= cte &

\end{flalign*}

\end{document}