I have solve this problem.
We render a text with latex using the comand line and it looks fine, so probably it was a problem in the comunication between moodle and my operating system, espicifically in the scape character.
So after googling a lite bit I solved. Everytime that you write some latex code betwenn $$ symbols, the first time thah you use de symbol '&' you need to add before it the symbol '^' so at the ends will looke like '^&'.
You need to do this only with the first & symbol that appers, if you doit twice new render problems will apper and its really tedius to get read of them. I will post here the two different version of the code (without the $$ symbols) so you can see the diference:
ORIGINAL TEXT:
\begin{tabular}{|c|c|c|c|c|c|c|c|} \hline \bf{x} &-1 & 0 & 1 & 2 & 3 \\ \hline \bf{y}& 2 & -1 & -4 & -25 & -82 \\ \hline \end{tabular} \\
CORRECTED TEXT:
\begin{tabular}{|c|c|c|c|c|c|c|c|} \hline \bf{x} ^&-1 & 0 & 1 & 2 & 3 \\ \hline \bf{y}& 2 & -1 & -4 & -25 & -82 \\ \hline \end{tabular} \\
I have put in red, bold and in big size the symbol '^' so you can note the difference. This solve the problem for me, hope it works for everybody else.
Sebatián Espinosa
from Chile!!!!