I would like to have a table like this:
% Preview source code
%% LyX 2.0.6 created this file. For more info, see http://www.lyx.org/.
%% Do not edit unless you really know what you are doing.
\documentclass[spanish,english]{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\makeatletter
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% LyX specific LaTeX commands.
%% Because html converters don't know tabularnewline
\providecommand{\tabularnewline}{\\}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% User specified LaTeX commands.
\usepackage{lipsum}
\usepackage{array}
\newcolumntype{C}{>{\centering\arraybackslash}m{10em}}
\usepackage{amsmath}
\makeatother
\usepackage{babel}
\addto\shorthandsspanish{\spanishdeactivate{~<>}}
\begin{document}
\selectlanguage{spanish}%
\begin{center}
\begin{table}
\begin{centering}
\begin{tabular}[b]{|c|C|C|C|}
\hline
Fkrmula & \multicolumn{3}{c|}{$\frac{2\alpha}{\beta+5.4\cos{\left(\pi\gamma\right)}}$}\tabularnewline
\hline
Error & \multicolumn{3}{c|}{$\sqrt{4\left\lvert {\frac{\Delta_{\alpha}}{\beta+5.4\cos{\left(\pi\gamma\right)}}}\right\rvert ^{2}+4\left\lvert {\frac{\Delta_{\beta}\alpha}{\left(\beta+5.4\cos{\left(\pi\gamma\right)}\right)^{2}}}\right\rvert ^{2}+116.64\pi^{2}\left\lvert {\frac{\Delta_{\gamma}\alpha\sin{\left(\pi\gamma\right)}}{\left(\beta+5.4\cos{\left(\pi\gamma\right)}\right)^{2}}}\right\rvert ^{2}}$ }\tabularnewline
\hline
Variable & $\beta$ & $\gamma$ & $\alpha$\tabularnewline
\hline
Valor & $1.02$ & $0.600$ & $5.0$\tabularnewline
\hline
Error & $0.10$ & $0.006$ & $0.5$\tabularnewline
\hline
Error en resultado & $2.4$ & $2.3$ & $1.5$\tabularnewline
\hline
Error total & \multicolumn{3}{c|}{$3.7$}\tabularnewline
\hline
Resultado & \multicolumn{3}{c|}{$-15\pm4$}\tabularnewline
\hline
\end{tabular}
\par\end{centering}
\caption{Errores}
\end{table}
\par\end{center}\selectlanguage{english}%
\end{document}
Where the three small columns are evenly split. I have tried this solution, but columns are only approximately equal when I set the correct parameter of the width. The problem us that I don't know what's going to be inside the cells (as the tables are autogenerated) nor the number of columns, and don't want to manually set the width every time; ie, there can be longer or shorter formulas in the second row and the number of var columns can be different for each table.
Ideally, the resulting table should be editable in the normal lyx gui (not ERT).
Also, I'd like to have more vertical spacing for the formulas.
