Matrices transformation from Programming Game AI By Examples

I know most of you have read Programming game ai by examples, so you know that in chapter 3 he uses matrices transformation to rotate his game agent. Unfortunately I’m one of those people who don’t know what a matrix is or why did he use a 3×3 matrices? Can anyone share a link or something about matrices and how to rotate a triangle agent just like from the book.


Link to Full Article: Matrices transformation from Programming Game AI By Examples