I got this error, after I copied and pasted the code below and changed the values. I don't know what's wrong with it.

Here's the code without the [ MATH] header

\left[\begin{array}{ccc}1&0&0\\0&1&0\\-1/3&0&1\right] \left[\begin{array}{ccc}3&1&1\\0&8/3&2/3\\1&1&3\end{array}\right]