math-mode – How to Use Nested Align without Extra Spacing in LaTeX

Question

I am trying to align the + symbols, while also aligning the = symbols, as such

As you can see, I managed to align at the ='s but not the +'s, how can I do that? This is the code I used (using quad to kind of align them):

                x &= a + b (ert)\\
            &\quad\quad + c(ert)\\
            &= abc

When I try something like this:

            x &= a &&+ b (ert)\\
            & &&+ c(ert)\\
            &= abc

I get this:

I also tried alignat, and split inside align, but nothing seems to do the trick.

Answer 1

You could use alignat but as you want the wrapped summation to overlap the abc on the last row, a nested aligned is better

\documentclass{article}

\usepackage{amsmath}

\begin{document}

alignat
\begin{alignat}{-1}
    x &= a &&+ b (ert)\\
      &    &&+ c(ert)\nonumber\\
      &= abc  
\end{alignat}

aligned
\begin{align}
    x &=\begin{aligned}[t]
         a &+ b (ert)\\
           &+ c(ert)
         \end{aligned}\\
      &= abc  
\end{align}

\end{document}