Matrix scale decomposition

I want to extract the scale of a matrix, but I don’t know how… Somebody could help me, please?

Use a matrix decompose routine, of course:
http://www.acm.org/tog/GraphicsGems/gemsii/unmatrix.c

You may want to get to know the Graphics Gems site:
http://www.acm.org/tog/GraphicsGems/

-Blake