[Algorithms] Rotation Matrices

[<Nik...@ao...>]

Why isn't the multiplication of rotational matrices commutative?  For example 
if I have one rotation matrix which rotates 20 degrees around the Z axis, and 
another which rotates 50 degrees around the X axis, depending on the order in 
which I multiply them, I get different results.  Why is this?  When rotating 
an object there is no visible difference when it is first rotated on one axis 
and then on another, is there?  I first looked in an elementary linear 
algebra book for the answer; however it stated that the multiplication of 
rotation matrices is commutative (although it was only covering 2D rotation 
matrices). Any help would be appreciated.

Thanks,
Nik...@ao...