#+OPTIONS: tex:t

$a = x \times y$ is rendered as Mathjax.
$a \coloneqq b$ is rendered wrong.

For large environment, use org babel for rendering.
#+header: :exports results :file test.png :results value raw file append
#+header: :imagemagick yes :iminoptions -density 600  -trim :imoutoptions -geometry 400 
#+header: :fit yes :headers '("\\usepackage{algorithmic}")
#+begin_src latex
\begin{algorithmic}
\REPEAT
\STATE $ \theta_j \coloneqq \theta_j - \alpha \frac{\partial}{\partial \theta_j} J(\theta_0,\theta_1) $ \COMMENT{for \(j = 0\) and \(j = 1\)}
\UNTIL{convergence}
\end{algorithmic}
#+end_src