title: how to represent rotation around 3D axis as a rotation around an fixed axis and what is the angle of the rotation
body: <p>I want to know where is the equation for 3D rotation come from?(http://en.wikipedia.org/wiki/Rotation_matrix). and if I want to rotate a point first around x axis for thetax degree, then rotate around y axis for thetay degree, at last rotate around z axis for thetaz degree, I want to ask: how to define the ux, uy, and uz in the above equation?</p>
  
  <p>and how to compute the theta in the equation?</p>
  
  <p>thanks for reading</p>