Solved!
the problem was in pi symbol,
when using the pi from the Greek's lyx menu (π) maxima did not understand(

) the symbol and returns the same expression.
when i change the Pi symbol with the 3.14 maxima has return the correct output.
Thank you very much for your time and answers!
and the result:
Code: Select all
\lim_{n\rightarrow\infty}\left(\frac{\sin\left(\frac{n\cdot\pi}{3}\right)}{n^{2}}\right)&=&\lim_{n\rightarrow\infty}{\frac{\sin\left(\frac{n\,\pi}{3}\right)}{n^{2}}}
\hspace{10 mm}
\lim_{n\rightarrow\infty}\left(\frac{\sin\left(n\cdot3.14\right)}{n^{2}}\right) =0

- lim.png (2.5 KiB) Viewed 9303 times
Is it a way to make maxima understand pi from LyX?