[Tex/LaTex] How to deal with big equations

alignequationsgathernestingsplit

I have a system of equations where the equations are big (one line isn't enough). I found this solution (the second one, from egreg How to align a set of very long equations) to manage the "how to align long equations ?" problem but I still have some troubles.

My equations are "just" sums of different elements, and some of these elements are big products (again, one line isn't enough).

Example (how to show the result of this code ?)

\documentclass[a4paper]{article}
\usepackage{amsmath}

\begin{document}
\begin{align}
    \begin{split}
        A &= AAAAAAAAAAAAAAAAAAAAAA \cdots \\
        &\qquad -BBBBBBBBBBBB\cdots\\
        & +\\
        &\qquad CCCCCCCCCCCCCCCCCCCCCCCCC\\
        & \times\\
        &\qquad CCCCCCCCCCCCCCCCCCCCCCCCCCCCC
    \end{split}
    \begin{split}
        A &= AAAAAAAAAAAAAAAAAAAAAA \cdots \\
        &\qquad -BBBBBBBBBBBB\cdots\\
        & +\\
        &\qquad CCCCCCCCCCCCCCCCCCCCCCCCC\\
        & \times\\
        &\qquad CCCCCCCCCCCCCCCCCCCCCCCCCCCCC
    \end{split}
\end{align}
\end{document}

What are the conventions in this case ?
If it's possible, I want to center the + and x and maybe add brackets for (CCCC x CCCC) to show it's only one element of the sum.
I suppose I have to nest an environment in one other but I don't know which environments.

I tried some things without success, but it may help you to understand what I mean
Try 1

\documentclass[a4paper]{article}
\usepackage{amsmath}

\begin{document}
\begin{align}
    \begin{split}
        A &= AAAAAAAAAAAAAAAAAAAAAA \cdots \\
        &\qquad -BBBBBBBBBBBB\cdots\\
        & \center{+}\\
        \left\(\begin{split}
            &\qquad CCCCCCCCCCCCCCCCCCCCCCCCC\\
            & \center{\times}\\
            &\qquad CCCCCCCCCCCCCCCCCCCCCCCCCCCCC
        \end{split}\right\)
    \end{split}
\end{align}
\end{document}

Try 2

\documentclass[a4paper]{article}
\usepackage{amsmath}

\begin{document}
\begin{align}
    \begin{split}
        A &= AAAAAAAAAAAAAAAAAAAAAA \cdots \\
        &\qquad -BBBBBBBBBBBB\cdots\\
        & \center{+}\\
        \left\(\begin{gather}
            \qquad CCCCCCCCCCCCCCCCCCCCCCCCC\\
             \center{\times}\\
            \qquad CCCCCCCCCCCCCCCCCCCCCCCCCCCCC
        \end{gather}\right\)
    \end{split}
\end{align}
\end{document}

EDIT :

As requested : here are some pictures to show what I have in mind. It may be no standard and if so, please tell me what is the "right" way.

Output of what I want

And an example of a true equation.

enter image description here

The first one doesn't have multiplicative symbol and a term is too long. But if I add the symbols and cut automatically the equation (Use equation and cases for big and numerous equation) the equation is less clear.

EDIT 2
As requested : here is the code to reproduce the "real" problem (not the equations I showed)

\documentclass[a4paper]{article}
\usepackage{amsmath}

\begin{document}

\begin{align}
    \begin{split}
        \dot{\text{R5P}} =& \nu_\text{maxVG6PDH}\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}} \\
        +& \nu_\text{maxVG6PDH}\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}} \\
        -& \nu_\text{maxVG6PDH}\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}} \\
    \end{split}\\
    \begin{split}
        \dot{\text{R5P}} =& \nu_\text{maxVG6PDH}\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}} \\
        +& \nu_\text{maxVG6PDH}\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}} \\
        -& \nu_\text{maxVG6PDH}\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}}\cdot\frac{G6P}{K_{mG6P}^{VG6PDH}} \\
    \end{split}
\end{align}

\end{document}

Best Answer

It is very hard to guess the intended output from the code shown. The code below runs without error and produces the following slightly odd looking output, which hopefully will give you a start in the right direction.

enter image description here

\documentclass[a4paper]{article}
\usepackage{mathtools}

\begin{document}
\begin{align*}
        A &= AAAAAAAAAAAAAAAAAAAAAA \cdots \\
        &\qquad -BBBBBBBBBBBB\cdots\\
        &+\\
        &\left(\begin{gathered}
            CCCCCCCCCCCCCCCCCCCCCCCCC\\
             \times\\
             CCCCCCCCCCCCCCCCCCCCCCCCCCCCC
    \end{gathered}\right)
\end{align*}
\end{document}
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