I don't know so much about cell display in SAGE cloud...but I guess... there are step s:
1. cell content in ASCII raw text is processed by Tex
2. tex content is then displayed by Mathjax
I am sure about Mathjax because I can mouse right button click on the displayed matrix in my browser (currently Chrome) and I get
one menu about Mathjax renderer (can be HTML-CSS, Mathml or SVG ; I cannot use MathMl because my browser has not brwser extension to display mathml ; SVG is my default display)
With the menu "show math as / tex commands" I get :
{x= \left(\begin{array}{rr}
1 & 2 \\
3 & 4
\end{array}\right)}
That means that default commands (set by new command) have been already parsed by Tex before send to Mathjax.
I can advice you to check is your browser can parse Mathjax commands : go to URL www.mathjax.org with your browser, to check if you have nice display |
of math upper right in the windo w. If not, check Javascript is ok.
If ok, then try to use various things in the SAGE cloud : first try to process a TEX file ; second search in one terminal is tex working for your projects; third, use the %latex tag in one cell