I am reading about direction of cosines which it seems to tie into change of axial system(transform of one coordinate system to another) and its just not clicking in my head. I don't know if its the text of the math book or what. I get the idea its how rotational matrices are generated from the angles passed in to make each one.
If anyone has insight on this it would be greatly appreciated (unfortunately wolfram and Wikipedia speak in language like this book does).