The way I make sense of these rotation matrices is to think about: If I am rotating around the x-axis, the x coordinate of the point will not change, and the resulted object has nothing to do with the x coordinate. Thus, the rotation matrix has its first column and row to be identity like, just to make sure x coordinate does not change and rotation does not involve x coordinate.
The way I make sense of these rotation matrices is to think about: If I am rotating around the x-axis, the x coordinate of the point will not change, and the resulted object has nothing to do with the x coordinate. Thus, the rotation matrix has its first column and row to be identity like, just to make sure x coordinate does not change and rotation does not involve x coordinate.