Deficiency in the article? 
It seems to me that there's a major deficiency in this article, which is that it's not made clear what the connection is between a rotation matrix and the geometric operation of rotation  this connection being that if you premultiply a rotation matrix by a column vector, then the result is another column vector that is just a rotation of the first.

Okay, it is stated eventually, but not until the geometry section, and there only in the abstract language of linear algebra, putting the main point of rotation matrices out of reach of anyone except those who should know it already.

I'm hesitating to jump in and revise it, as I'm kind of new to linear algebra, but will probably go ahead and take a crack at it eventually if no one with more expertise wants to step up.

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