[Tex/LaTex] Equations lining up and labeling

equations

I'm trying to line up multiple equations next to each other and have
them all properly labeled. There is another question discussing
this exact problem. Unfortunately, all the solutions proposed there
produce output with the equations sitting on different baselines,
which is extremely jarring.

Here's the document I'm working with:

\documentclass{article}
\usepackage{amsmath, amsfonts}
\begin{document}
\begin{equation}
  \mathbf{a} \cdot \mathbf{b} = \sum_{i=1}^n a_ib_i
  \qquad
  \mathbf{a} \cdot \mathbf{b} =
    \lVert \mathbf{a} \rVert
    \lVert \mathbf{b} \rVert \cos \theta
\end{equation}
\end{document}

When written this way, it appears that both left-hand sides use the
same baseline and the output looks quite pleasing. Unfortunately I
couldn't achieve the same effect using the suggestions from the linked
question (which are tabularx, multicol or minipage).

Please help!

Update.
I realize that the question is a bit poorly worded. What I really want here, is an ability to arrange equations on a grid, in a way similar to how various align environments work, but at the same time also labeling equations that end up on the same row. I hope that makes sense.

Best Answer

The minipage solution from the question you linked to can actually be used here, provided that you supply the second minipage with an optional [b] argument (the argument can be t for top, c for center, b, see parboxes on tug and minipages on tug for more details).

screenshot

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


\noindent\begin{minipage}{.5\textwidth}
\begin{equation}
  \mathbf{a} \cdot \mathbf{b} = \sum_{i=1}^n a_ib_i
\end{equation}
\end{minipage}%
\begin{minipage}[b]{.5\textwidth}
 \begin{equation}
  \mathbf{a} \cdot \mathbf{b} =
    \lVert \mathbf{a} \rVert
    \lVert \mathbf{b} \rVert \cos \theta
\end{equation}
\end{minipage}
\end{document}

Following the updated question and the comments, here is an example of how you can use the above idea in a tabular* environment

screenshot2

\documentclass[draft]{article}
\usepackage{amsmath, amsfonts}

\newenvironment{minipeqn}[1][]{\begin{minipage}[#1]{.45\textwidth}\begin{equation}}{\end{equation}\end{minipage}}
\begin{document}

\noindent\begin{tabular*}{\textwidth}{ll}
 \begin{minipeqn}
  \mathbf{a} \cdot \mathbf{b} = \sum_{i=1}^n a_ib_i
\end{minipeqn}&
\begin{minipeqn}[b]
  \mathbf{a} \cdot \mathbf{b} =
    \lVert \mathbf{a} \rVert
    \lVert \mathbf{b} \rVert \cos \theta
\end{minipeqn}\\
\begin{minipeqn}
  \mathbf{a} \cdot \mathbf{b} = \sum_{i=1}^n a_ib_i
\end{minipeqn}&
 \begin{minipeqn}[b]
  \mathbf{a} \cdot \mathbf{b} =
    \lVert \mathbf{a} \rVert
    \lVert \mathbf{b} \rVert \cos \theta
\end{minipeqn}\\
\begin{minipeqn}
  \mathbf{a} \cdot \mathbf{b} = \sum_{i=1}^n a_ib_i
\end{minipeqn}&
 \begin{minipeqn}[b]
  \mathbf{a} \cdot \mathbf{b} =
    \lVert \mathbf{a} \rVert
    \lVert \mathbf{b} \rVert \cos \theta
\end{minipeqn}
\end{tabular*}

\end{document}
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