MathJax Test 2

basic test...
$$ \cos^2\theta-\sin^2\theta=\cos 2\theta $$

matrices....
The characteristic polynomial $\chi(\lambda)$ of the $3 \times 3$ matrix
\[ \left( \begin{array}{ccc}
a & b & c \\
d & e & f \\
g & h & i \end{array} \right) \]

partials & matrices...
\[ \frac{1}{i} \frac{ \partial }{ \partial \theta_{x}} \begin{pmatrix}
R_{11} & R_{12} &R_{13} \\
R_{21} & R_{22} & R_{23}\\
R_{31} & R_{32} & R_{33}
\end{pmatrix} \]

neat.