mathURL
http://mathurl.com/6n3vevw
<img src="http://mathurl.com/6n3vevw.png" />
![\left[ \begin{array}{cccc} x & -y & x_0 \\ y & x & y_0 \\ 0 & 0 & 1 \end{array} \right]\left[ \begin{array}{cccc} x' \\ y' \\ 1 \end{array} \right]](http://mathurl.com/6n3vevw.png)